The canonical source_selection setting was rendering as a free-text box — easy
to typo an invalid mode. Added a generic choice mechanism so it's a dropdown:
- RepairJob.setting_options: {key: [allowed values]} (default {} — opt-in).
- CanonicalVersionResolveJob declares source_selection's three modes.
- repair_worker.get_all_job_info() includes setting_options in the job payload.
- enrichment.js renders a <select> (options prettified, current value selected)
for any key listed in setting_options; everything else renders by value type
as before. The save path already reads <select>.value as a string, so no
change needed there.
Generic — any future job can get dropdowns the same way. Jobs that don't
declare setting_options are untouched (empty dict -> existing input rendering).
Tests: source_selection exposes the 3 options and its default is one of them.
23 repair-job/worker + canonical tests pass (other jobs unaffected).
dfa5204e0a