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/modules/integration/services/zimbra.ts

@@ -0,0 +1,21 @@
+import type { ZimbraSettings, ZimbraSettingsWrite, ZimbraTestResult } from './dto/zimbra'
+
+export function useZimbraService() {
+    const api = useApi()
+
+    async function getSettings(): Promise<ZimbraSettings> {
+        return api.get<ZimbraSettings>('/settings/zimbra')
+    }
+
+    async function saveSettings(payload: ZimbraSettingsWrite): Promise<ZimbraSettings> {
+        return api.put<ZimbraSettings>('/settings/zimbra', payload as Record<string, unknown>, {
+            toastSuccessKey: 'zimbra.settings.saved',
+        })
+    }
+
+    async function testConnection(): Promise<ZimbraTestResult> {
+        return api.post<ZimbraTestResult>('/settings/zimbra/test', {})
+    }
+
+    return { getSettings, saveSettings, testConnection }
+}