feat(ai): wire up workspace RAG bulk reindex + manual "Reindex now"

The WORKSPACE_CREATE_EMBEDDINGS / WORKSPACE_DELETE_EMBEDDINGS jobs were
enqueued (on AI Search enable/disable) but had no AI_QUEUE handler, so
existing pages were never indexed ("Indexed 0 of N pages") and disabling
never purged embeddings.

- EmbeddingProcessor: handle WORKSPACE_CREATE_EMBEDDINGS (bulk reindex all
  live pages) and WORKSPACE_DELETE_EMBEDDINGS (purge workspace embeddings)
- EmbeddingIndexerService: add reindexWorkspace() (skips when embeddings
  unconfigured; per-page error isolation) and removeWorkspace()
- PageRepo.getIdsByWorkspace(), PageEmbeddingRepo.deleteByWorkspace()
- AiSettingsService.reindex() + admin-only POST /workspace/ai-settings/reindex
- Frontend: "Reindex now" button, service call and mutation
- Stable per-workspace jobId with remove-before-add so a stale job can't
  block future reindexes; cancel the delayed purge on enable/reindex so it
  can't wipe freshly-built embeddings

apps/server/src/database/repos/ai-chat/page-embedding.repo.ts

@@ -70,6 +70,21 @@ export class PageEmbeddingRepo {
       .execute();
   }
 
+  /**
+   * HARD-delete every embedding row for an entire workspace. Used when AI Search
+   * is disabled for the workspace (WORKSPACE_DELETE_EMBEDDINGS).
+   */
+  async deleteByWorkspace(
+    workspaceId: string,
+    trx?: KyselyTransaction,
+  ): Promise<void> {
+    const db = dbOrTx(this.db, trx);
+    await db
+      .deleteFrom('pageEmbeddings')
+      .where('workspaceId', '=', workspaceId)
+      .execute();
+  }
+
   /**
    * Bulk-insert chunk rows for a page. The `embedding` value is serialized with
    * `pgvector.toSql` and cast to `vector` so Postgres stores it in the

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

@@ -195,6 +195,20 @@ export class PageRepo {
     return Number(row?.count ?? 0);
   }
 
+  /**
+   * IDs of all non-deleted pages in a workspace. Used by the RAG bulk reindex to
+   * (re)build embeddings for every existing page.
+   */
+  async getIdsByWorkspace(workspaceId: string): Promise<string[]> {
+    const rows = await this.db
+      .selectFrom('pages')
+      .select('id')
+      .where('workspaceId', '=', workspaceId)
+      .where('deletedAt', 'is', null)
+      .execute();
+    return rows.map((r) => r.id);
+  }
+
   async deletePage(pageId: string): Promise<void> {
     let query = this.db.deleteFrom('pages');