fix: winit + softbuffer for layout-agnostic input and better FPS

Replaced minifb with winit + softbuffer:

Input (layout-agnostic):
- winit uses PhysicalKey<KeyCode> which maps to physical key positions
- KeyCode::KeyA = physical A key, regardless of keyboard layout
- Works on Russian, Arabic, any layout — no key mapping needed
- HashSet<KeyCode> tracks pressed/released state
- Proper Press/Release events from OS, no timeout hacks

FPS improvements:
- Glyph atlas pre-built at startup (alpha bitmap, zero per-frame alloc)
- render_to_buffer: skip empty cells entirely (no draw call)
- blend_fast: bitshift instead of division for alpha blending
- Buffer fill via .fill() instead of nested loop
- copy_from_slice for pixel transfer to softbuffer (memcpy speed)
- ControlFlow::Poll for maximum frame rate

109 tests, 0 failures

Cargo.toml

@@ -8,8 +8,10 @@ crossterm = "0.28"
 clap = { version = "4", features = ["derive"] }
 serde = { version = "1", features = ["derive"] }
 serde_json = "1"
-minifb = "0.27"
 fontdue = "0.9"
+winit = "0.30"
+softbuffer = "0.4"
+log = "0.4"
 
 [profile.release]
 opt-level = 3