Fix P1 accessibility issues in Button and Card

Button:
- Add aria-busy={loading} for assistive technology
- Add visually-hidden "Loading" text for screen readers
- Mark CircularProgress as aria-hidden (decorative)

Card:
- Add tabIndex={0} and role="button" when interactive
- Fix Record<string, any> → Theme type for type safety

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

src/components/atoms/Button/Button.tsx

@@ -50,6 +50,7 @@ export const Button = React.forwardRef<HTMLButtonElement, ButtonProps>(
         variant={variant}
         size={size}
         disabled={loading || disabled}
+        aria-busy={loading || undefined}
         sx={[
           underline &&
             variant === 'text' && {
@@ -63,12 +64,30 @@ export const Button = React.forwardRef<HTMLButtonElement, ButtonProps>(
       >
         {children}
         {loading && (
+          <>
             <CircularProgress
               size={16}
               color="inherit"
               thickness={3}
+              aria-hidden
               sx={{ ml: 1 }}
             />
+            <span
+              style={{
+                position: 'absolute',
+                width: 1,
+                height: 1,
+                padding: 0,
+                margin: -1,
+                overflow: 'hidden',
+                clip: 'rect(0, 0, 0, 0)',
+                whiteSpace: 'nowrap',
+                borderWidth: 0,
+              }}
+            >
+              Loading
+            </span>
+          </>
         )}
       </MuiButton>
     );

src/components/atoms/Card/Card.tsx

@@ -2,6 +2,7 @@ import React from 'react';
 import MuiCard from '@mui/material/Card';
 import type { CardProps as MuiCardProps } from '@mui/material/Card';
 import CardContent from '@mui/material/CardContent';
+import type { Theme } from '@mui/material/styles';
 
 // ─── Types ───────────────────────────────────────────────────────────────────
 
@@ -56,11 +57,17 @@ export const Card = React.forwardRef<HTMLDivElement, CardProps>(
     // Map FA variant names to MUI Card variant
     const muiVariant = variant === 'outlined' ? 'outlined' : undefined;
 
+    // Interactive cards need keyboard operability
+    const interactiveProps = interactive
+      ? { tabIndex: 0 as const, role: 'button' as const }
+      : {};
+
     return (
       <MuiCard
         ref={ref}
         variant={muiVariant}
         elevation={0}
+        {...interactiveProps}
         sx={[
           // Selected state: brand border + warm background
           // Border width is always 2px (set in theme) — only colour changes here
@@ -81,7 +88,7 @@ export const Card = React.forwardRef<HTMLDivElement, CardProps>(
           // Focus-visible for keyboard accessibility on interactive cards
           interactive && {
             '&:focus-visible': {
-              outline: (theme: Record<string, any>) =>
+              outline: (theme: Theme) =>
                 `2px solid ${theme.palette.primary.main}`,
               outlineOffset: '2px',
             },