Introduces candy-gloss tile rendering (diagonal gradient + glass highlight
+ optional glow) via a shared paintGlossyTile() in tile_painter.dart,
applied to board filled-cells and tray/drag-overlay pieces. Adds
ThemeColors to palette.dart for UI-layer season color resolution, and
activeThemeProvider for one-call access to the active season's theme.
Regenerates the game_screen golden to reflect the new look.
airkjw
8739fc0e26