feat: signal when chat runs complete

Users can miss chat completions while the app is in the background.

They can also miss completions when their attention is elsewhere.

Add opt-out sound notifications and a temporary title marker.

This makes completion noticeable without external audio assets or persistent browser notifications.

src/components/chat/hooks/useChatRealtimeHandlers.ts

@@ -2,6 +2,8 @@ import { useEffect, useRef } from 'react';
 import type { Dispatch, MutableRefObject, SetStateAction } from 'react';
 
 import { usePaletteOps } from '../../../contexts/PaletteOpsContext';
+import { showCompletionTitleIndicator } from '../../../utils/pageTitleNotification';
+import { playChatCompletionSound } from '../../../utils/notificationSound';
 import type { PendingPermissionRequest, SessionNavigationOptions } from '../types/types';
 import type { ProjectSession, LLMProvider } from '../../../types/app';
 import type { SessionStore, NormalizedMessage } from '../../../stores/useSessionStore';
@@ -285,6 +287,9 @@ export function useChatRealtimeHandlers({
           break;
         }
 
+        showCompletionTitleIndicator();
+        void playChatCompletionSound();
+
         const actualSessionId =
           typeof msg.actualSessionId === 'string' && msg.actualSessionId.trim().length > 0
             ? msg.actualSessionId