Fix P2 audit issues in ProviderCard — image a11y, token compliance

- Add role="img" + aria-label to hero image for screen readers
- Logo shadow: hardcoded rgba → var(--fa-shadow-sm)
- Logo border: hardcoded white → var(--fa-color-white) for theme consistency
- Audit score: 17/20 (Good), 0 P0/P1, 3 P2 fixed, 3 P3 noted

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

src/components/molecules/ProviderCard/ProviderCard.tsx

@@ -131,6 +131,8 @@ export const ProviderCard = React.forwardRef<HTMLDivElement, ProviderCardProps>(
         {/* ── Image area (verified only) ── */}
         {showImage && (
           <Box
+            role="img"
+            aria-label={`Photo of ${name}`}
             sx={{
               position: 'relative',
               height: IMAGE_HEIGHT,
@@ -167,8 +169,8 @@ export const ProviderCard = React.forwardRef<HTMLDivElement, ProviderCardProps>(
                   borderRadius: LOGO_BORDER_RADIUS,
                   objectFit: 'cover',
                   backgroundColor: 'background.paper',
-                  boxShadow: '0 2px 8px rgba(0,0,0,0.15)',
-                  border: '2px solid white',
+                  boxShadow: 'var(--fa-shadow-sm)',
+                  border: '2px solid var(--fa-color-white)',
                 }}
               />
             )}