perf: reduce history content paint polling from 120 to 30 RAF attempts

The history overlay polling calls isTurnTextRenderedInViewport() up to 120 times (nearly 2 seconds). Reduced to 30 attempts (~500ms) which is still sufficient for typical content paint latency.

Author: kev1n77

src/web-ui/src/flow_chat/components/modern/ModernFlowChatContainer.history-state.test.tsx

@@ -578,15 +578,15 @@ describe('ModernFlowChatContainer historical empty state', () => {
       root.render(<ModernFlowChatContainer />);
     });
 
-    for (let index = 0; index < 120; index += 1) {
+    for (let index = 0; index < 30; index += 1) {
       flushAnimationFrame();
     }
 
     expect(container.textContent).not.toContain('Loading saved session');
     expect(releaseSpy).not.toHaveBeenCalled();
     expect(startupTraceMock.markPhase).toHaveBeenCalledWith(
       'historical_session_initial_content_paint_signal_missed',
-      expect.objectContaining({ attempts: 120 }),
+      expect.objectContaining({ attempts: 30 }),
     );
 
     releaseSpy.mockRestore();

src/web-ui/src/flow_chat/components/modern/ModernFlowChatContainer.tsx

@@ -89,7 +89,7 @@ type BackgroundCommandSummary = {
 };
 
 const LATEST_TURN_AUTO_PIN_MAX_ATTEMPTS = 8;
-const HISTORY_INITIAL_CONTENT_PAINT_MAX_ATTEMPTS = 120;
+const HISTORY_INITIAL_CONTENT_PAINT_MAX_ATTEMPTS = 30;
 const MOCK_BACKGROUND_ACTIVITIES_STORAGE_KEY = 'bitfun.flowChat.mockBackgroundActivities';
 
 const MOCK_BACKGROUND_SUBAGENTS: BackgroundSubagentSummary[] = [