feat(identity-wallet): add alert badge to identity cards
Add alert status display on identity cards in IdentityListHome:
- Fetch alert status via checkIdentityStatus() on mount
- Listen for plc_alert events from background monitoring
- Render red alert badge when alertCount > 0
- Make alert badge clickable to navigate to alert detail
- Add onalert callback prop for parent handling
Verifies: plc-key-management.AC6.4 (alert badge display)