feat(integration) : extract Gitea/BookStack/Zimbra/Share front into module layer

LST-68 (2.6) front. Completes the Integration module and Phase 2.

- New frontend/modules/integration/ layer (auto-detected): services
  (gitea, bookstack, zimbra, share, share-settings) + their DTOs, and the
  useShareStatus composable.
- Consumers repointed to ~/modules/integration/...: admin tabs
  (Gitea/BookStack/Zimbra/Share), PM task sections (TaskGitSection,
  TaskBookStackLinks, TaskDocumentShareLinker), ProjectDrawer, TaskModal,
  pages/documents.vue, components/share/SharedFilePreview.vue.
- Admin tabs, SharedFilePreview and documents/admin pages stay at their
  location (only imports updated). i18n stays global.

nuxt build passes; all routes preserved.

frontend/components/admin/AdminZimbraTab.vue

@@ -58,7 +58,7 @@
 </template>
 
 <script setup lang="ts">
-import { useZimbraService } from '~/services/zimbra'
+import { useZimbraService } from '~/modules/integration/services/zimbra'
 
 const { getSettings, saveSettings, testConnection } = useZimbraService()