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/components/ErrorBoundary.vue

@@ -0,0 +1,37 @@
+<script setup lang="ts">
+import { ref, onErrorCaptured } from 'vue'
+import { AlertTriangle } from 'lucide-vue-next'
+
+const hasError = ref(false)
+const errorMessage = ref('')
+
+onErrorCaptured((err) => {
+  hasError.value = true
+  errorMessage.value = err.message || 'An unexpected error occurred'
+  console.error('ErrorBoundary caught:', err)
+  return false
+})
+
+function retry() {
+  hasError.value = false
+  errorMessage.value = ''
+  window.location.reload()
+}
+</script>
+
+<template>
+  <div v-if="hasError" class="min-h-screen bg-neutral-950 flex items-center justify-center p-6">
+    <div class="bg-neutral-900 border border-neutral-800 rounded-lg p-8 max-w-md w-full text-center">
+      <AlertTriangle class="w-12 h-12 text-red-500 mx-auto mb-4" />
+      <h1 class="text-xl font-bold text-neutral-100 mb-2">Something went wrong</h1>
+      <p class="text-sm text-neutral-400 mb-6">{{ errorMessage }}</p>
+      <button
+        @click="retry"
+        class="px-4 py-2 bg-oxide-500 hover:bg-oxide-600 text-white font-medium rounded-lg transition-colors"
+      >
+        Retry
+      </button>
+    </div>
+  </div>
+  <slot v-else />
+</template>