Three render modes:
- --mode terminal: pure ANSI ASCII in terminal
- --mode ascii: Vulkan window with ASCII characters (glyph atlas)
- --mode graphics: Vulkan window with colored cells (no glyphs, each
material = unique base color, no lighting yet)
Graphics renderer:
- Same Vulkan pipeline as ASCII but without glyph atlas
- Simpler shaders: graphics.vert/frag just output instance color
- No descriptor set, no texture sampling
- Each cell = colored quad, material color fills entire cell
- Entities rendered as colored shapes (player=yellow, goblin=green)
Default mode changed to --mode ascii
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