feat(server): skip cleanup for stale workspace (#13418)

fix AI-408

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* Added a new field to workspaces to track the last time embeddings were
checked.
* Cleanup jobs for workspace embeddings now skip workspaces that haven't
changed in over 30 days or have no embeddings, improving efficiency.
* Cleanup jobs are now automatically triggered when a workspace is
updated.

* **Improvements**
* Enhanced workspace selection for cleanup and indexing tasks to use
more precise filters and batching.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/backend/server/src/plugins/indexer/job.ts

@@ -157,10 +157,12 @@ export class IndexerJob {
     }
 
     const startSid = payload.lastIndexedWorkspaceSid ?? 0;
-    const workspaces = await this.models.workspace.listAfterSid(
-      startSid,
+    const workspaces = await this.models.workspace.list(
+      { sid: { gt: startSid } },
+      { id: true, indexed: true, sid: true },
       this.config.indexer.autoIndex.batchSize
     );
+
     if (workspaces.length === 0) {
       // Keep the current sid value when repeating
       return JOB_SIGNAL.Repeat;