feat(chess): Make Chess Professional — opening names, material count, move classification, PGN sharing

Pro features added:
- Opening name display: shows ECO opening name during game (40+ openings in Arabic/English)
- Material count difference: shows +2/-1 advantage next to captured pieces
- Move classifier engine: labels moves as brilliant(!!) / great(!) / best(★) / good / book / inaccuracy(?!) / mistake(?) / blunder(??)
- Accuracy calculator: 0-100% accuracy score based on move classifications
- Material counter: tracks piece values for both sides from FEN
- PGN Share: share button uses Web Share API or clipboard
- PGN Copy: one-tap copy to clipboard with visual feedback

Foundation for remaining features:
- classifier.js ready for post-game analysis integration
- openings.js ready for opening explorer
- material.js ready for in-game display
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>