batch3 T5: frontend foundation — Pane types, panes API, user-events WS

- Mirror Pane/PaneState/UserStream types
- api.panes.* CRUD methods
- sessionEvents adds session_updated, session_loaded, open_file_in_browser
- useUserEvents hook: single app-level WS to /api/ws/user with reconnect
- useSidebar handles session_updated (in-place patch + re-sort) and
  session_loaded (active-project highlight gap fix); open_file_in_browser
  is a deliberate no-op here, consumed by Workspace later
- App.tsx mounts useUserEvents once

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/web/src/App.tsx

@@ -4,21 +4,29 @@ import { Home } from '@/pages/Home';
 import { Project } from '@/pages/Project';
 import { Session } from '@/pages/Session';
 import { Toaster } from '@/components/ui/sonner';
+import { useUserEvents } from '@/hooks/useUserEvents';
+
+function AppShell() {
+  useUserEvents();
+  return (
+    <div className="dark h-screen flex bg-background text-foreground">
+      <ProjectSidebar />
+      <main className="flex-1 flex flex-col min-w-0">
+        <Routes>
+          <Route path="/" element={<Home />} />
+          <Route path="/project/:id" element={<Project />} />
+          <Route path="/session/:id" element={<Session />} />
+        </Routes>
+      </main>
+      <Toaster position="bottom-right" />
+    </div>
+  );
+}
 
 export default function App() {
   return (
     <BrowserRouter>
-      <div className="dark h-screen flex bg-background text-foreground">
-        <ProjectSidebar />
-        <main className="flex-1 flex flex-col min-w-0">
-          <Routes>
-            <Route path="/" element={<Home />} />
-            <Route path="/project/:id" element={<Project />} />
-            <Route path="/session/:id" element={<Session />} />
-          </Routes>
-        </main>
-        <Toaster position="bottom-right" />
-      </div>
+      <AppShell />
     </BrowserRouter>
   );
 }