Add selected prop to ProviderCard

Thread Card's selected state (brand border + warm bg) through
ProviderCard for the radiogroup selection pattern in ProvidersStep.

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

src/components/molecules/ProviderCard/ProviderCard.tsx

@@ -37,6 +37,8 @@ export interface ProviderCardProps {
   capabilityDescription?: string;
   /** Starting price in dollars (shown as "From $X") */
   startingPrice?: number;
+  /** Whether this card is the currently selected provider */
+  selected?: boolean;
   /** Click handler — entire card is clickable */
   onClick?: () => void;
   /** MUI sx prop for style overrides */
@@ -96,6 +98,7 @@ export const ProviderCard = React.forwardRef<HTMLDivElement, ProviderCardProps>(
       capabilityLabel,
       capabilityColor = 'default',
       capabilityDescription,
+      selected = false,
       startingPrice,
       onClick,
       sx,
@@ -109,6 +112,7 @@ export const ProviderCard = React.forwardRef<HTMLDivElement, ProviderCardProps>(
       <Card
         ref={ref}
         interactive
+        selected={selected}
         padding="none"
         onClick={onClick}
         sx={[