feat(frontend): Implement client-side SSE handling (#35)

Implements real-time event streaming on the frontend with:

- Event types and type guards matching backend EventType enum
- Zustand-based event store with per-project buffering
- useProjectEvents hook with auto-reconnection and exponential backoff
- ConnectionStatus component showing connection state
- EventList component with expandable payloads and filtering

All 105 tests passing. Follows design system guidelines.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/lib/stores/index.ts

@@ -3,5 +3,14 @@
 
 export { useAuthStore, initializeAuth, type User } from './authStore';
 
+// Event Store for SSE events
+export {
+  useEventStore,
+  useProjectEventsFromStore,
+  useLatestEvent,
+  useEventCount,
+  type EventStore,
+} from './eventStore';
+
 // Authentication Context (DI wrapper for auth store)
 export { useAuth, AuthProvider } from '../auth/AuthContext';