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/dto/bookstack.ts

@@ -0,0 +1,42 @@
+export type BookStackSettings = {
+    url: string | null
+    hasToken: boolean
+}
+
+export type BookStackSettingsWrite = {
+    url: string | null
+    tokenId: string | null
+    tokenSecret: string | null
+}
+
+export type BookStackTestResult = {
+    success: boolean
+}
+
+export type BookStackShelf = {
+    id: number
+    name: string
+}
+
+export type BookStackLink = {
+    id: number
+    bookstackId: number
+    bookstackType: 'page' | 'book'
+    title: string
+    url: string
+    createdAt: string
+}
+
+export type BookStackLinkCreate = {
+    bookstackId: number
+    bookstackType: 'page' | 'book'
+    title: string
+    url: string
+}
+
+export type BookStackSearchResult = {
+    id: number
+    type: 'page' | 'book'
+    name: string
+    url: string
+}