Orphaned Assets Fix

[yugalkaushik]

Issue:

Completes #4107

This change adds a pending-upload workflow for user assets so files are not permanently stored until a project is successfully saved. It also adds rollback for failed clones and a scheduled cleanup path for abandoned pending uploads. Uploaded assets now go to a pending S3 prefix first, are committed into the final user/project location on save, and are removed later if they stay pending too long. The cleanup threshold is 7 days, and the server checks for stale pending assets once every 24 hours.

Demo:

preview-orphanedassets.mp4

Changes:

• Uploads are signed into pending/{userId}/... using the authenticated user id.
• Project creation and project updates both commit any pending assets after a successful save.
• Clone failures delete copied S3 assets so partial clone attempts do not leave leftovers behind.
• A scheduled cleanup job scans for stale pending assets and deletes them after the retention window.
• Pending uploads are kept for 7 days before they become eligible for cleanup.
• The cleanup job runs every 24 hours, so stale pending assets are removed automatically without requiring a manual save or manual cleanup.

I have verified that this pull request:

• has no linting errors (npm run lint)
• has no test errors (npm run test)
• has no typecheck errors (npm run typecheck)
• is from a uniquely-named feature branch and is up to date with the develop branch.
• is descriptively named and links to an issue number, i.e. Fixes #123
• meets the standards outlined in the accessibility guidelines