feat: Frontend gap closure — Schedules, Alerts, Migration, Changelog views

Implements missing frontend views and API integrations:

New Views:
- SchedulesView: CRUD for scheduled tasks (restart/announcement/command/plugin_reload)
- MigrationView: Export/import interface with file upload and history tracking
- ChangelogView: Paginated changelog feed with category badges
- ForgotPasswordView: Password reset flow with email submission
- AlertsView: Alert config dashboard with threshold settings and history

Component Updates:
- ErrorBoundary: Global error handler with retry functionality
- DashboardLayout: Mobile responsive sidebar, permission-based nav, new menu items
- ServerInfoView: Complete rewrite for public server info display

Infrastructure:
- useApi: Token refresh interceptor with 401 retry and infinite loop prevention
- plugins store: Implemented all stubbed methods with real API calls
- auth store: Added hasPermission() helper for RBAC UI visibility
- Router: Added new routes with catch-all fallback

Purpose: Closes frontend implementation gaps. Hardens auth flow, improves mobile UX,
enables server automation scheduling, alert configuration, and data migration tools.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/App.vue

@@ -1,9 +1,12 @@
 <script setup lang="ts">
 import { RouterView } from 'vue-router'
 import ToastNotification from '@/components/ToastNotification.vue'
+import ErrorBoundary from '@/components/ErrorBoundary.vue'
 </script>
 
 <template>
   <ToastNotification />
-  <RouterView />
+  <ErrorBoundary>
+    <RouterView />
+  </ErrorBoundary>
 </template>