Fix coursework document storage lifecycle

[Linda-riziki]

Summary

This PR fixes the coursework document storage lifecycle by improving the security and consistency of uploaded files.

Changes

• Made the coursework storage bucket private.
• Replaced public file URLs with private storage paths.
• Added secure access to coursework files using server-side/signed retrieval.
• Updated document deletion to remove both the database record and the storage object.
• Added retry handling for failed storage cleanup.
• Added a reconciliation script to identify and clean up orphaned or missing storage records.
• Added a coursework retention policy.
• Added migration and storage lifecycle test scripts.

Testing

• Verified the application builds and runs locally.
• Reviewed the upload and delete flows to ensure they use private storage paths and clean up storage correctly.
• End-to-end upload testing could not be completed because uploads require a paid credit.

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Project	Deployment	Actions	Updated (UTC)
skills-sync	Ready	Preview, Comment	Jul 28, 2026 12:40pm