fix AI-408
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## 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.
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