Bug 1: Resign not detected - endGame now skips redundant complete API call
when server already completed the match (resign/draw/abandon via poll).
Bug 2: Players seeing themselves as opponent - verify and correct color
from authoritative server match data on game start.
Bug 3: Checkmate not appearing - send final move to server BEFORE calling
endGame so opponent receives the checkmate FEN position.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>