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/composables/useShareStatus.ts

@@ -1,23 +0,0 @@
-import { useShareService } from '~/services/share'
-
-export function useShareStatus() {
-    const enabled = useState<boolean | null>('share-enabled', () => null)
-    const { getStatus } = useShareService()
-
-    async function refresh() {
-        try {
-            const status = await getStatus()
-            enabled.value = status.enabled
-        } catch {
-            enabled.value = false
-        }
-    }
-
-    async function ensureLoaded() {
-        if (enabled.value === null) {
-            await refresh()
-        }
-    }
-
-    return { enabled, refresh, ensureLoaded }
-}