* test(share): add failing tests for Delete ownership checks
* fix(share): add ownership check to Delete
* test(share): add failing tests for Update ownership checks
* fix(share): add ownership check to Update
* refactor(share): extract checkOwnership helper with lightweight query
- Deduplicate ownership check from Delete and Update into a single helper
- Use a minimal single-column SELECT instead of Get (avoids loadMedia overhead)
- Use positive bypass form (IsAdmin || invalidUserId) matching codebase convention
* fix(share): convert model.ErrNotFound to rest.ErrNotFound in checkOwnership
Ensure consistent 404 responses when a nonexistent share ID is passed
to Delete or Update, by handling the conversion in checkOwnership
rather than relying on the subsequent write operation.
6b8fcc37c6