* 🧯 fix: Remove revoked agents from user favorites
When agent access is revoked, the agent remained in the user's favorites
causing repeated 403 errors on page load. Backend now cleans up favorites
on permission revocation; frontend treats 403 like 404 and auto-removes
stale agent references.
* 🧪 fix: Address review findings for stale agent favorites cleanup
- Guard cleanup effect with ref to prevent infinite loop on mutation
failure (Finding 1)
- Use validated results.revoked instead of raw request payload for
revokedUserIds (Finding 3)
- Stabilize staleAgentIds memo with string key to avoid spurious
re-evaluation during drag-drop (Finding 5)
- Add JSDoc with param types to removeRevokedAgentFromFavorites
(Finding 7)
- Return promise from removeRevokedAgentFromFavorites for testability
- Add 7 backend tests covering revocation cleanup paths
- Add 3 frontend tests for 403 handling and stale cleanup persistence
