feat(app): top-level error boundary so a render error no longer blanks the app (#1194)

* feat(app): add a top-level error boundary so a render error no longer blanks the app

Until now any thrown error during render took the whole window down with no recovery (issue #382). A class ErrorBoundary around the authenticated shell catches it and shows a recoverable fallback (Try again / Reload app) while playback keeps going. Hook-free + English-only with literal CSS var() fallbacks so it renders even when i18n/theme/state is what broke.

* docs(changelog): error boundary prevents the app blanking on a render error (PR #1194)

src/app/MainApp.tsx

@@ -32,6 +32,7 @@ import { useMigrationOrchestrator } from '../hooks/useMigrationOrchestrator';
 import { IS_WINDOWS } from '../utils/platform';
 import TauriEventBridge from './TauriEventBridge';
 import AppShell from './AppShell';
+import ErrorBoundary from '../components/ErrorBoundary';
 import BlockingMigrationGate from './BlockingMigrationGate';
 import RequireAuth from './RequireAuth';
 import { useMigrationStore } from '../store/migrationStore';
@@ -191,9 +192,11 @@ export default function MainApp() {
                 path="/*"
                 element={
                   <RequireAuth>
-                    <DragDropProvider>
-                      <AppShell />
-                    </DragDropProvider>
+                    <ErrorBoundary>
+                      <DragDropProvider>
+                        <AppShell />
+                      </DragDropProvider>
+                    </ErrorBoundary>
                   </RequireAuth>
                 }
               />