feat(07-uat): admin AI panel UX enhancements + DocumentCard status indicators

- GET /api/admin/ai-config/models — fetch model list from provider's /models endpoint
- POST /api/admin/ai-config/test-connection — replaced GET; accepts unsaved form
  values (api_key, base_url, model_name) so admins can test before saving
- TestConnectionRequest Pydantic model with provider_id validation
- SearchableModelSelect.vue — new reusable combobox; Teleport to body avoids
  overflow:hidden clipping; shows all models on open, filters only on typing;
  static "Enter manually" item always pinned at bottom; caches per provider
- AdminAiConfigTab: model name input replaced with SearchableModelSelect;
  testingProvider ref + spinner added to Test Connection button
- DocumentCard: processing spinner + "Classifying…", pending "Queued" badge,
  classification_failed badge; topics section only shown when status=ready
- FileManagerView: onUnmounted imported (polling wiring pending next session)

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

frontend/src/views/FileManagerView.vue

@@ -44,7 +44,7 @@
 </template>
 
 <script setup>
-import { ref, reactive, computed, watch, onMounted } from 'vue'
+import { ref, reactive, computed, watch, onMounted, onUnmounted } from 'vue'
 import { useRoute, useRouter } from 'vue-router'
 import { useFoldersStore } from '../stores/folders.js'
 import { useDocumentsStore } from '../stores/documents.js'