PoC pixel-art mode

[skhoroshavin]

Proof of concept: when the Phaser game's pixelArt config flag is set, MSDF text switches to plain bitmap rendering - atlases upload with NEAREST filtering and the shader reads coverage straight from the texel alpha instead of the distance field. Everything in one draw call, as before.

What should work:

• Rich text end to end: per-run colors/alpha, per-run fonts (incl. merged atlases), fontScale, kerning, wrap
• Underline / strikethrough / highlight pills / dashed rules unchanged (they are shader-drawn rects, not texture data)
• Hard drop shadows (offset silhouette); glyph substitution, transforms, deform, all callbacks

What is disabled (one-time console warning if someone still tries to enable them):

• Weight, outline in all forms, soft/spread/rounded shadows, two-tone ramps - all distance-field based

What is left:

• Update to the actual demo
• Actual testing - there might still be edge cases, especially related to rounding or absence of it