- Add AUTO_ACCEPT_THRESHOLD_V2 = 0.80 constant to objective_backfill.py
- Add min_threshold param to find_match_candidates() (default REVIEW_THRESHOLD=0.6)
- Add match_method param to auto_apply_matches() (default 'fuzzy_trgm')
- Add ?v2=true query param to POST /api/v1/admin/etl/objective-backfill
- v2 mode: threshold=0.80, method='fuzzy_v2', search from 0.80 (not 0.60)
- Return type widened to dict[str,object] to include threshold_used + match_method_used
DB audit: 1068 unmapped EKB objs; v1 adds ~133 rows, v2 adds ~47 more.
Expected coverage: 8.5% → ~20% after sequential v1+v2 runs on prod.
Run: POST /objective-backfill (v1) then POST /objective-backfill?v2=true (v2).
Part of task #44 Part A, epic #271.
