Let owners review dense speaker candidate pairs
Owners can now review acoustically similar dense speaker candidates from Suggestions with per-side audio evidence and stable anchor-based dismissal that survives candidate id churn.
Accepting one of these suggestions performs a speaker candidate-pool merge, not an entity merge, and the curation response reports that the merge has no undo. Also wire the speakers suggestion generator and formatter for the new kind and rename the new store writer to record_candidate_pair.