feat: crash recovery — global error handlers + toast + burst-reload

- lib/crashRecovery.ts: window.onerror + unhandledrejection handlers,
  dedupe identical messages within 10s, burst-reload after 8 distinct
  errors in 30s
- components/CrashToast.tsx: portal stack in bottom-right, max 3 visible,
  auto-dismiss after 7s, per-entry close button
- Wired in main.tsx before bootstrap so crypto/i18n errors are captured,
  rendered from App.tsx alongside UpdateToast

Covers the async layer ErrorBoundary misses (realtime handlers, stray
Promises, setTimeout callbacks, LiveKit listeners).

apps/desktop/src/App.tsx

@@ -1,6 +1,7 @@
 import { BrowserRouter, Navigate, Outlet, Route, Routes } from 'react-router-dom';
 
 import { AppShell } from './components/AppShell';
+import { CrashToast } from './components/CrashToast';
 import { ErrorBoundary } from './components/ErrorBoundary';
 import { UpdateToast } from './components/UpdateToast';
 import { RequireAdmin, RequireAuth, RequireDevice } from './components/guards';
@@ -91,6 +92,7 @@ export function App() {
                     <Route path="*" element={<Navigate to="/chats" replace />} />
                   </Routes>
                   <UpdateToast />
+                  <CrashToast />
                 </BrowserRouter>
               </CallProvider>
             </ConversationsProvider>