- Duplicate-tag create/rename hit the uq_tags_user_name constraint and 500'd; now caught and
returned as a clear 409 ('You already have a tag named …').
- New global error dialog (errorDialog store + ErrorDialog modal) for definitive server refusals;
the api layer wiring + mount land with the rest of the round.
- Modal now keeps a stack so ESC dismisses only the top modal — an error over the tag editor
closes the error and leaves the editor open.
