fix: wrap mockOnClose in act() to fix flaky LiveLogViewer test

Fixes race condition where WebSocket disconnect event wasn't being
processed within React's rendering cycle, causing intermittent CI
failures. Wrapping mockOnClose() in act() ensures React state updates
are flushed before assertions run.

Resolves #237

frontend/src/components/__tests__/LiveLogViewer.test.tsx

@@ -321,7 +321,9 @@ describe('LiveLogViewer', () => {
 
     await waitFor(() => expect(screen.getByText('Connected')).toBeTruthy());
 
-    mockOnClose?.();
+    act(() => {
+      mockOnClose?.();
+    });
 
     await waitFor(() => expect(screen.getByText('Disconnected')).toBeTruthy());
   });