- Wrap DELETE + INSERTs in a database transaction via new
ReplaceEnvVarsByAppID() to prevent silent data loss on partial
insert failure. Rollback on any error; return 500 instead of 200.
- Add server-side validation rejecting entries with empty keys
(returns 400 with error message).
- Add frontend error handling for non-2xx responses with user-visible
alert messages.
- Remove stale //nolint:dupl directives (files no longer duplicate).