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/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',
             },