feat: window mode with minifb — direct keyboard polling, no terminal

New --mode window (now default):
- minifb creates a real OS window (no terminal needed)
- fontdue rasterizes DejaVu Sans Mono glyphs to pixel buffer
- ASCII characters rendered as colored pixels — same aesthetic
- Keyboard polled via get_pressed_keys() every frame:
  - Instant response, no terminal delay
  - Proper multi-key support (W+A strafing works)
  - No Release event hacks needed
  - No key repeat timeout hacks
  - Instant stop when key released

Controls: WASD/arrows, 1-9/0 paint, X erase, HJKL camera, Q/Esc quit
--mode terminal still available as fallback

109 tests, 0 warnings, 0 failures

src/render/window_input.rs

@@ -0,0 +1,60 @@
+use minifb::Key;
+
+pub struct WindowInput {
+    pub left: bool,
+    pub right: bool,
+    pub jump: bool,
+    pub cam_left: bool,
+    pub cam_right: bool,
+    pub cam_up: bool,
+    pub cam_down: bool,
+    pub quit: bool,
+    pub paint: Option<u8>,
+}
+
+impl WindowInput {
+    pub fn new() -> Self {
+        Self {
+            left: false, right: false, jump: false,
+            cam_left: false, cam_right: false, cam_up: false, cam_down: false,
+            quit: false, paint: None,
+        }
+    }
+
+    pub fn update(&mut self, keys: &[Key]) {
+        let was_jump = self.jump;
+        let now_left = keys.contains(&Key::A) || keys.contains(&Key::Left);
+        let now_right = keys.contains(&Key::D) || keys.contains(&Key::Right);
+        let now_jump = keys.contains(&Key::W) || keys.contains(&Key::Space) || keys.contains(&Key::Up);
+        let now_cam_left = keys.contains(&Key::H);
+        let now_cam_right = keys.contains(&Key::L);
+        let now_cam_up = keys.contains(&Key::K);
+        let now_cam_down = keys.contains(&Key::J);
+
+        self.left = now_left && !now_right;
+        self.right = now_right && !now_left;
+        if now_left && now_right {
+            self.left = false;
+            self.right = false;
+        }
+        self.jump = now_jump && !was_jump;
+        self.cam_left = now_cam_left;
+        self.cam_right = now_cam_right;
+        self.cam_up = now_cam_up;
+        self.cam_down = now_cam_down;
+        self.quit = keys.contains(&Key::Q) || keys.contains(&Key::Escape);
+
+        self.paint = None;
+        if keys.contains(&Key::Key1) { self.paint = Some(1); }
+        else if keys.contains(&Key::Key2) { self.paint = Some(2); }
+        else if keys.contains(&Key::Key3) { self.paint = Some(3); }
+        else if keys.contains(&Key::Key4) { self.paint = Some(4); }
+        else if keys.contains(&Key::Key5) { self.paint = Some(5); }
+        else if keys.contains(&Key::Key6) { self.paint = Some(6); }
+        else if keys.contains(&Key::Key7) { self.paint = Some(7); }
+        else if keys.contains(&Key::Key8) { self.paint = Some(8); }
+        else if keys.contains(&Key::Key9) { self.paint = Some(9); }
+        else if keys.contains(&Key::Key0) { self.paint = Some(0); }
+        else if keys.contains(&Key::X) { self.paint = Some(99); }
+    }
+}