feat(ai-chat): show RAG indexing coverage in AI settings

Display "Indexed N of M pages" on the AI provider settings page so admins
can see how much of the wiki is covered by vector-RAG semantic search.

- page-embedding.repo: add countIndexedPages() — distinct non-deleted pages
  that have stored embeddings in the workspace
- page.repo: add countByWorkspace() — total non-deleted pages
- ai-settings.service: compute both counts in getMasked() (Promise.all) and
  return them with the masked settings; inject PageEmbeddingRepo + PageRepo
- MaskedAiSettings / IAiSettings: add indexedPages + totalPages
- ai-provider-settings: render a dimmed coverage line under "Embedding model"
- i18n: add the "Indexed {{indexed}} of {{total}} pages" key (en-US, ru-RU)

apps/server/src/database/repos/page/page.repo.ts

@@ -181,6 +181,20 @@ export class PageRepo {
     return result;
   }
 
+  /**
+   * Count non-deleted pages in a workspace. Used by the AI settings page to show
+   * RAG indexing coverage ("N of M pages indexed").
+   */
+  async countByWorkspace(workspaceId: string): Promise<number> {
+    const row = await this.db
+      .selectFrom('pages')
+      .where('workspaceId', '=', workspaceId)
+      .where('deletedAt', 'is', null)
+      .select((eb) => eb.fn.countAll().as('count'))
+      .executeTakeFirst();
+    return Number(row?.count ?? 0);
+  }
+
   async deletePage(pageId: string): Promise<void> {
     let query = this.db.deleteFrom('pages');