Add AddOnOption molecule — toggleable add-on with Switch

- Composes Card (interactive, selected) + Typography + Switch
- Maps to Figma ListItemAddItem (2350:40658) — toggle for optional extras
- Heading + optional price + description + Switch right-aligned
- Selected state via Card brand border + warm bg when checked
- Clicking anywhere on card toggles the switch (stopPropagation on switch)
- aria-labelledby connects switch to heading text
- 7 stories: Default, Checked, ServiceAddOns (interactive list with total),
  WithoutPrice, WithoutDescription, Disabled, EdgeCases

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/components/molecules/AddOnOption/AddOnOption.stories.tsx

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+import React from 'react';
+import type { Meta, StoryObj } from '@storybook/react';
+import { AddOnOption } from './AddOnOption';
+import Box from '@mui/material/Box';
+import Typography from '@mui/material/Typography';
+import Divider from '@mui/material/Divider';
+
+const meta: Meta<typeof AddOnOption> = {
+  title: 'Molecules/AddOnOption',
+  component: AddOnOption,
+  tags: ['autodocs'],
+  parameters: {
+    layout: 'centered',
+    design: {
+      type: 'figma',
+      url: 'https://www.figma.com/design/XUDUrw4yMkEexBCCYHXUvT/Parsons?node-id=2350-40658',
+    },
+  },
+  argTypes: {
+    name: { control: 'text' },
+    description: { control: 'text' },
+    price: { control: 'number' },
+    checked: { control: 'boolean' },
+    disabled: { control: 'boolean' },
+  },
+  decorators: [
+    (Story) => (
+      <Box sx={{ width: 480 }}>
+        <Story />
+      </Box>
+    ),
+  ],
+};
+
+export default meta;
+type Story = StoryObj<typeof AddOnOption>;
+
+// ─── Default ────────────────────────────────────────────────────────────────
+
+/** Default — unchecked add-on with description */
+export const Default: Story = {
+  args: {
+    name: 'Memorial video',
+    description:
+      'Professional video tribute played during the service, compiled from family photos and footage.',
+    price: 350,
+  },
+};
+
+// ─── Checked ────────────────────────────────────────────────────────────────
+
+/** Checked — add-on is enabled, card shows selected state */
+export const Checked: Story = {
+  args: {
+    name: 'Memorial video',
+    description:
+      'Professional video tribute played during the service, compiled from family photos and footage.',
+    price: 350,
+    checked: true,
+  },
+};
+
+// ─── Service Add-Ons ────────────────────────────────────────────────────────
+
+/** Realistic — arrangement flow add-ons list */
+export const ServiceAddOns: Story = {
+  render: function Render() {
+    const [addOns, setAddOns] = React.useState({
+      catering: false,
+      video: true,
+      flowers: false,
+      transport: false,
+      webcast: false,
+    });
+
+    const toggle = (key: keyof typeof addOns) => (checked: boolean) =>
+      setAddOns({ ...addOns, [key]: checked });
+
+    const total = [
+      addOns.catering ? 1200 : 0,
+      addOns.video ? 350 : 0,
+      addOns.flowers ? 280 : 0,
+      addOns.transport ? 450 : 0,
+      addOns.webcast ? 150 : 0,
+    ].reduce((a, b) => a + b, 0);
+
+    return (
+      <Box sx={{ display: 'flex', flexDirection: 'column', gap: 2 }}>
+        <Typography variant="h5">Optional extras</Typography>
+        <Typography variant="body2" color="text.secondary">
+          Customise the service with additional options. All prices are GST inclusive.
+        </Typography>
+
+        <Box sx={{ display: 'flex', flexDirection: 'column', gap: 1.5 }}>
+          <AddOnOption
+            name="Catering"
+            description="Light refreshments for up to 50 guests after the service."
+            price={1200}
+            checked={addOns.catering}
+            onChange={toggle('catering')}
+          />
+          <AddOnOption
+            name="Memorial video"
+            description="Professional video tribute compiled from family photos and footage."
+            price={350}
+            checked={addOns.video}
+            onChange={toggle('video')}
+          />
+          <AddOnOption
+            name="Floral arrangements"
+            description="Casket spray and two standing arrangements for the chapel."
+            price={280}
+            checked={addOns.flowers}
+            onChange={toggle('flowers')}
+          />
+          <AddOnOption
+            name="Premium transport"
+            description="Vintage hearse and one family limousine for the procession."
+            price={450}
+            checked={addOns.transport}
+            onChange={toggle('transport')}
+          />
+          <AddOnOption
+            name="Live webcast"
+            description="Stream the service online for family and friends who cannot attend."
+            price={150}
+            checked={addOns.webcast}
+            onChange={toggle('webcast')}
+          />
+        </Box>
+
+        <Divider />
+
+        <Box sx={{ display: 'flex', justifyContent: 'space-between', alignItems: 'baseline' }}>
+          <Typography variant="label" color="text.secondary">
+            Extras total
+          </Typography>
+          <Typography variant="h6" color="primary">
+            ${total.toLocaleString('en-AU')}
+          </Typography>
+        </Box>
+      </Box>
+    );
+  },
+};
+
+// ─── Without Price ──────────────────────────────────────────────────────────
+
+/** No price — some add-ons are complimentary */
+export const WithoutPrice: Story = {
+  args: {
+    name: 'Order of service booklet',
+    description: 'Complimentary printed booklet with the service programme and a photo of your loved one.',
+  },
+};
+
+// ─── Without Description ────────────────────────────────────────────────────
+
+/** No description — compact variant for simple toggles */
+export const WithoutDescription: Story = {
+  render: function Render() {
+    const [checked, setChecked] = React.useState(false);
+    return (
+      <AddOnOption
+        name="Include GST in pricing"
+        checked={checked}
+        onChange={setChecked}
+      />
+    );
+  },
+};
+
+// ─── Disabled ───────────────────────────────────────────────────────────────
+
+/** Disabled — add-on unavailable (e.g. venue restriction) */
+export const Disabled: Story = {
+  args: {
+    name: 'Catering',
+    description: 'Not available at this venue. Please contact the venue directly for catering options.',
+    price: 1200,
+    disabled: true,
+  },
+};
+
+// ─── Edge Cases ─────────────────────────────────────────────────────────────
+
+/** Edge cases — long text, high prices, missing fields */
+export const EdgeCases: Story = {
+  render: function Render() {
+    const [checks, setChecks] = React.useState({ a: false, b: true, c: false });
+
+    return (
+      <Box sx={{ display: 'flex', flexDirection: 'column', gap: 1.5 }}>
+        <AddOnOption
+          name="Premium memorial video with extended family interview package and professional editing"
+          description="Our most comprehensive video tribute including on-site filmed interviews with family members, professional editing with music selection, up to 20 minutes of curated content, plus a USB copy and online streaming access for 12 months."
+          price={2500}
+          checked={checks.a}
+          onChange={(v) => setChecks({ ...checks, a: v })}
+        />
+        <AddOnOption
+          name="Flowers"
+          checked={checks.b}
+          onChange={(v) => setChecks({ ...checks, b: v })}
+        />
+        <AddOnOption
+          name="Complimentary parking"
+          description="Reserved parking for family vehicles at the venue."
+          price={0}
+          checked={checks.c}
+          onChange={(v) => setChecks({ ...checks, c: v })}
+        />
+      </Box>
+    );
+  },
+};

src/components/molecules/AddOnOption/AddOnOption.tsx

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+import React from 'react';
+import Box from '@mui/material/Box';
+import type { SxProps, Theme } from '@mui/material/styles';
+import { Card } from '../../atoms/Card';
+import { Typography } from '../../atoms/Typography';
+import { Switch } from '../../atoms/Switch';
+
+// ─── Types ───────────────────────────────────────────────────────────────────
+
+/** Props for the FA AddOnOption molecule */
+export interface AddOnOptionProps {
+  /** Add-on name/heading */
+  name: string;
+  /** Description text explaining the add-on */
+  description?: string;
+  /** Price in dollars — shown after the heading */
+  price?: number;
+  /** Whether this add-on is currently enabled */
+  checked?: boolean;
+  /** Called when the toggle changes */
+  onChange?: (checked: boolean) => void;
+  /** Whether this add-on is disabled/unavailable */
+  disabled?: boolean;
+  /** MUI sx prop for style overrides */
+  sx?: SxProps<Theme>;
+}
+
+// ─── Component ───────────────────────────────────────────────────────────────
+
+/**
+ * Toggleable add-on option for the FA design system.
+ *
+ * Used in the arrangement flow for optional extras — catering, memorial
+ * video, flowers, transport upgrades, etc. Users toggle the switch to
+ * include or exclude; multiple add-ons can be active simultaneously.
+ *
+ * Composes Card + Typography + Switch. Maps to the Figma
+ * "ListItemAddItem" component (desktop + mobile viewports).
+ *
+ * For mutually exclusive options (single-select), use ServiceOption instead.
+ *
+ * Usage:
+ * ```tsx
+ * <AddOnOption
+ *   name="Memorial video"
+ *   description="Professional video tribute played during the service."
+ *   price={350}
+ *   checked={addOns.memorialVideo}
+ *   onChange={(on) => setAddOns({ ...addOns, memorialVideo: on })}
+ * />
+ * ```
+ */
+export const AddOnOption = React.forwardRef<HTMLDivElement, AddOnOptionProps>(
+  ({ name, description, price, checked = false, onChange, disabled = false, sx }, ref) => {
+    const switchId = React.useId();
+
+    const handleToggle = () => {
+      if (!disabled && onChange) {
+        onChange(!checked);
+      }
+    };
+
+    const handleSwitchChange = (_e: React.ChangeEvent<HTMLInputElement>, value: boolean) => {
+      if (onChange) {
+        onChange(value);
+      }
+    };
+
+    return (
+      <Card
+        ref={ref}
+        interactive={!disabled}
+        selected={checked}
+        padding="none"
+        onClick={handleToggle}
+        sx={[
+          {
+            p: 'var(--fa-card-padding-compact)',
+            cursor: disabled ? 'not-allowed' : 'pointer',
+            ...(disabled && {
+              opacity: 'var(--fa-opacity-disabled)',
+              pointerEvents: 'none' as const,
+            }),
+          },
+          ...(Array.isArray(sx) ? sx : [sx]),
+        ]}
+      >
+        {/* Heading row: name + optional price + switch */}
+        <Box
+          sx={{
+            display: 'flex',
+            alignItems: 'center',
+            justifyContent: 'space-between',
+            gap: 2,
+          }}
+        >
+          <Box sx={{ display: 'flex', alignItems: 'baseline', gap: 1, flex: 1, minWidth: 0 }}>
+            <Typography
+              variant="h6"
+              component="span"
+              id={`${switchId}-label`}
+            >
+              {name}
+            </Typography>
+            {price != null && (
+              <Typography
+                variant="body2"
+                color="text.secondary"
+                sx={{ whiteSpace: 'nowrap' }}
+              >
+                ${price.toLocaleString('en-AU')}
+              </Typography>
+            )}
+          </Box>
+
+          <Switch
+            checked={checked}
+            onChange={handleSwitchChange}
+            disabled={disabled}
+            onClick={(e) => e.stopPropagation()}
+            inputProps={{ 'aria-labelledby': `${switchId}-label` }}
+            sx={{ flexShrink: 0 }}
+          />
+        </Box>
+
+        {/* Description */}
+        {description && (
+          <Typography
+            variant="body2"
+            color="text.secondary"
+            sx={{ mt: 0.5 }}
+          >
+            {description}
+          </Typography>
+        )}
+      </Card>
+    );
+  },
+);
+
+AddOnOption.displayName = 'AddOnOption';
+export default AddOnOption;

src/components/molecules/AddOnOption/index.ts

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+export { AddOnOption } from './AddOnOption';
+export type { AddOnOptionProps } from './AddOnOption';