fix(dashboard): disable SSE in demo mode and remove unused hooks

- Skip SSE connection in demo mode (MSW doesn't support SSE).
- Remove unused `useProjectEvents` and related real-time hooks from `Dashboard`.
- Temporarily disable activity feed SSE until a global endpoint is available.

frontend/src/lib/hooks/useProjectEvents.ts

@@ -247,6 +247,15 @@ export function useProjectEvents(
    * Connect to SSE endpoint
    */
   const connect = useCallback(() => {
+    // In frontend demo mode (MSW), SSE is not supported - skip connection
+    if (config.demo.enabled) {
+      if (config.debug.api) {
+        console.log('[SSE] Demo mode enabled - SSE connections disabled');
+      }
+      updateConnectionState('disconnected');
+      return;
+    }
+
     // Prevent connection if not authenticated or no project ID
     /* istanbul ignore next -- early return guard, tested via connection state */
     if (!isAuthenticated || !accessToken || !projectId) {