[codex] Support current XCPC ELO upstream schema

[greenthree]

What changed

• Normalize the current XCPC ELO name/history payload into the internal player contract while retaining compatibility with the legacy teamMember/rating/contests shape.
• Derive current rating, peak rating, and contest count from the current history tuples.
• Add adapter and shared-cache regression coverage.
• Record the production recovery evidence in ROADMAP.md.

Root cause

The upstream XCPC ELO data.js schema changed from teamMember/rating/contests to name/history. The old parser classified the shared cache refresh as schema_changed, so downstream member synchronization safely retained stale values.

Validation

• Edge Function tests: 479 passed, 0 failed, 1 ignored.
• Targeted Deno checks: 40/40 passed.
• Vitest: 101 files, 648 tests passed.
• Formatting, lint, build, sync workflow checks, and git diff --check passed.
• Production sync-stats v40 and sync-member v59 are active.
• One controlled xcpc_elo run succeeded: 3 pages, 7/7 results succeeded.
• Cache recovered to v4 with 53 players and no error/cooldown; all 7 XCPC stats are fresh.
• QOJ had zero jobs, runs, and stats writes in the validation window.

No QOJ rerun, other function deployment, Secret/Vault change, database migration, or Pages deployment was performed for this recovery.