Chess board:
- Square colors now read from theme system (getColor) instead of hardcoded
  constants — editing board colors in admin branding instantly affects all
  modes (game, analysis, puzzles)

Logos:
- HUD brand text replaced with assetImg('logo') — shows uploaded PNG
- Splash screen uses logo image instead of text
- Favicon and apple-touch-icon added to index.php
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>