Design for source-binding + quality-aware fall-through ranking
(per-source population, source-priority-king), ranked-targets UI,
quarantine-reason surfacing, and tests. Locks the constraints that
quality quarantine reuses the trigger='quality' retry path and never
sets force_imported (reserved for AcoustID mismatches).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
