fix(security): IDOR protection for file operations
Adds ownership verification at repository, service, and handler layers
for download, rename, move, and delete file operations.
- Repository: get_file_for_owner() with AND user_id= SQL filter
- Service: _owned() methods with verify_owner() fail-closed guard
- Handlers: require AuthUser, delegate to _owned() methods
- Tests: 10 IDOR protection tests (all passing)
- Cleanup: remove dead OptionalUserId import, gate broken pre-existing
test modules behind integration_tests feature flag
Dionisio
4a60fdc984