Keep game view steps pixel exact under Windows display scaling

At 125% Windows scaling the game view drew 100% as 1.25 screen pixels
per camera pixel, so pixel art showed texels of uneven width even at
the round steps. The steps now count device pixels instead of CSS
pixels.

- gameScaleFactor, cameraFactor and cameraView take the device pixel
  ratio. 100% is one screen pixel per camera pixel, 200% two.
- Auto picks the largest step that fits in device pixels. Fit reports
  its factor in device pixels too, e.g. 156% at 125% scaling.
- Fixed steps start the frame on a whole device pixel.
- The game view reads the ratio from the renderer resolution.

Limits: main.ts caps the resolution at 2, so scaling above 200% is
stretched by the browser again. A changed ratio at runtime only counts
after a reload, as before.

Tests:
- 2 unit tests at 125%: 100% is one device pixel on a whole pixel,
  auto and fit count device pixels.
- Counter-check: without the conversion the 100% test fails.
- check.sh: 156 files, CHECK EXIT 0 on the combined working tree.
- No e2e: the harness runs at devicePixelRatio 1, same math as before.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/viewport/view.test.ts

@@ -88,6 +88,26 @@ describe('cameraView with a zoomed camera', () => {
   });
 });
 
+describe('cameraView under Windows scaling at 125%', () => {
+  const plain = { x: 0, y: 0, props: { width: 640, height: 360, zoom: 1 } };
+
+  it('100% is one device pixel per camera pixel, starting on a whole device pixel', () => {
+    const view = cameraView(plain, 801, 601, 1, 1.25);
+    expect(view.scale * 1.25).toBeCloseTo(1, 12);
+    expect(view.rect.w).toBeCloseTo(512, 12);
+    expect(view.rect.h).toBeCloseTo(288, 12);
+    expect(view.rect.x * 1.25).toBeCloseTo(181, 9);
+    expect(view.rect.y * 1.25).toBeCloseTo(196, 9);
+  });
+
+  it('auto picks the step in device pixels, and fit reports device pixels', () => {
+    expect(cameraFactor(plain.props, 1100, 700, 'auto', 1.25)).toBe(2);
+    expect(cameraFactor(plain.props, 1100, 700, 'auto')).toBe(1);
+    expect(cameraFactor(plain.props, 800, 600, 'fit', 1.25)).toBeCloseTo(1.5625, 9);
+    expect(cameraView(plain, 800, 600, 'fit', 1.25).scale).toBeCloseTo(1.25, 9);
+  });
+});
+
 describe('gameScaleFactor', () => {
   it('fit is the exact factor that fills the tighter side', () => {
     expect(gameScaleFactor('fit', 640, 360, 800, 600)).toBeCloseTo(1.25, 9);