No completed match in production has ever had white_rating_after or
rating_change_white written, and 272 of the 290 profiles were still sitting on
the default 1200. The complete_match database function does not touch the rating
columns, and game.php had calculateElo() and getRatingColumn() helpers that
nothing ever called.

Elo is now computed in applyRatings(), called from finaliseMatch() after its
conditional write has succeeded — so a game can never be rated twice. It writes
both ratings before and after and the deltas onto the match, updates the correct
per-time-control column on each profile along with the game/win/loss/draw and
streak counters, and records a rating_history row per player.

This matters beyond the leaderboard: Swiss seeding orders players by rating, so
with every rating pinned at 1200 the top-half/bottom-half split in round 1 was
arbitrary.

Bot games and aborted games are never rated, and a match with the same player on
both sides is refused outright.

Covered by e2e sections 18 and 19.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>