Make stable UFCStats identity authoritative end to end

[komaksym]

Parent

• Implement auditable UFC dataset fidelity pipeline #14 — Implement auditable UFC dataset fidelity pipeline

What to build

Make source identity and provenance authoritative from UFCStats ingestion through normalized/raw observations and incremental updates. Stable source IDs must replace name/date-based identity without collapsing rematches or hiding conflicting observations.

Acceptance criteria

• Scraped fight records retain fight_id, event_id, red/blue fighter IDs, source URLs, red/blue orientation, and source provenance.
• A newly scraped record without fight_id is a hard identity failure; identity_status=legacy_fallback is reserved for genuinely pre-ID historical records and remains visibly warning-level.
• IDs, names, result markers, and canonical outcomes (red_win, blue_win, draw, no_contest) remain aligned with the red/blue corners.
• Incremental merging is idempotent on stable fight_id and preserves same-card rematches.
• Identical stable-ID observations may coalesce deterministically while remaining visible in raw evidence; conflicting observations sharing a stable ID preserve every version and quarantine the conflict.
• Source-adapter and incremental-update fixtures cover missing IDs, legacy rows, rematches, repeated input, identical duplicates, and conflicting duplicates.

Blocked by

• None (can start immediately).