feat: log per-move deltas to matchLogs/{roomId}.moves[] (single-document array)

[ibloud]

Summary

Implement per-move stat capture in gameNamespace.js by writing move deltas into a single Firestore document at matchLogs/{roomId}, using an append-only moves array (not a subcollection).

Schema alignment

This issue follows docs/design/player-profile-schema.md:

• One parent document per match: matchLogs/{roomId}
• Per-move deltas stored in moves[] on that parent document
• Typical payload (~16KB) remains well below Firestore's 1MB document limit

Implementation

• On first confirmed make_move, create (or upsert) matchLogs/{roomId}.
• Ensure base fields exist (example):
  • roomId, createdAt, startedAt, players, completedAt, winner
  • moves: []
• After each confirmed move, append one entry to moves[] with:
  • moveNum, color, from, to, piece, capturedPiece
  • evalBefore, evalAfter, severity
  • veiled, veiledOpponent, sacrifice
  • inversionClause, promotedTo
  • timeMs, timestamp
• On gameOver=true, set:
  • completedAt
  • winner

Constraints

• moves[] must be append-only and preserve chronological order.
• Writes should be idempotent against duplicate move events (no duplicate moveNum entries).
• Keep document size under Firestore limits for expected match lengths.

Acceptance Criteria

• A completed remote match produces one readable matchLogs/{roomId} document.
• Per-move deltas are present in moves[] and ordered by moveNum.
• No subcollection is used for move logs.
• Finalization fields (completedAt, winner) are set on game completion.