Replace egui text rendering with a BitmapFont system:
- Glyph.tile: u32 replaces ch: char; top-left pixel of PNG is background sentinel
- BitmapFont loads/preprocesses PNG to opaque-white + transparent, tinted at render time
- Default font: assets/vga-font-8x16.png (CP437, 8×16 tiles); placeholder generated if missing
- Boards can specify a per-board font via [font] in their .toml file
- Editor Board tab: "Font…" button opens font dialog (rfd file picker, tile dims, tilesheet preview)
- Glyph picker: tile grid from active font replaces hardcoded ASCII char grid
- map_file: TileIndex untagged enum accepts char or integer in palette entries
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
randrews
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