feat: show active session name in browser tab title

Updates document.title dynamically to show the current session label
(e.g. 'main — PinchChat'). Integrates with the existing notification
system so unread badges still work correctly (e.g. '(3) main — PinchChat').
Resets to plain 'PinchChat' when no session is selected.

src/App.tsx

@@ -1,6 +1,6 @@
 import { useState, useEffect, useCallback, useRef, lazy, Suspense } from 'react';
 import { useGateway } from './hooks/useGateway';
-import { useNotifications } from './hooks/useNotifications';
+import { useNotifications, setBaseTitle } from './hooks/useNotifications';
 import { Header } from './components/Header';
 import { Sidebar } from './components/Sidebar';
 import { LoginScreen } from './components/LoginScreen';
@@ -33,6 +33,13 @@ export default function App() {
     }
   }, [messages, notify]);
 
+  // Update document title with active session label
+  useEffect(() => {
+    const session = sessions.find(s => s.key === activeSession);
+    setBaseTitle(session?.label || session?.key);
+    return () => setBaseTitle(undefined);
+  }, [activeSession, sessions]);
+
   // Close sidebar on Escape key, open shortcuts on ?
   const handleKeyDown = useCallback((e: KeyboardEvent) => {
     if (e.key === 'Escape' && sidebarOpen) {

src/hooks/useNotifications.ts

@@ -1,7 +1,17 @@
 import { useState, useEffect, useCallback, useRef } from 'react';
 import { playNotificationSound } from '../lib/notificationSound';
 
-const ORIGINAL_TITLE = document.title;
+const APP_NAME = 'PinchChat';
+let baseTitle = APP_NAME;
+
+/** Update the base title (e.g. with active session name). Called by App. */
+export function setBaseTitle(sessionLabel?: string) {
+  baseTitle = sessionLabel ? `${sessionLabel} — ${APP_NAME}` : APP_NAME;
+  // Refresh document.title if tab is visible (no unread badge)
+  if (!document.hidden) {
+    document.title = baseTitle;
+  }
+}
 const SOUND_KEY = 'pinchchat-notification-sound';
 const hasNotificationAPI = typeof Notification !== 'undefined';
 
@@ -25,7 +35,7 @@ export function useNotifications() {
       if (!document.hidden) {
         // Reset unread when tab becomes visible
         setUnreadCount(0);
-        document.title = ORIGINAL_TITLE;
+        document.title = baseTitle;
       }
     };
     document.addEventListener('visibilitychange', handleVisibility);
@@ -35,7 +45,7 @@ export function useNotifications() {
   // Update tab title when unread count changes
   useEffect(() => {
     if (unreadCount > 0) {
-      document.title = `(${unreadCount}) ${ORIGINAL_TITLE}`;
+      document.title = `(${unreadCount}) ${baseTitle}`;
     }
   }, [unreadCount]);