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>

src/editor/viewport/GameViewport.ts

@@ -6,7 +6,7 @@ import { type FederatedPointerEvent, Text } from 'pixi.js';
 import { isSymbolType } from '../../core/model/AssetTypes';
 import type { EditorState } from '../state';
 import type { World } from '../../runtime/World';
-import { textStyle } from '../../ui';
+import { textStyle, ui } from '../../ui';
 import { type ActiveCamera, cameraOfItems, cameraOfWorld } from '../../viewport/activeCamera';
 import { collectHolderItems, collectWorldItems } from '../../viewport/items';
 import {
@@ -31,7 +31,7 @@ export class GameViewport extends WorldViewport {
   private playWorld: World | null = null;
   /** The editor run's world: it takes the mouse, but it is never what this view draws. */
   private editorWorld: World | null = null;
-  /** Screen pixels per camera pixel as last drawn, null without a camera. */
+  /** Device pixels per camera pixel as last drawn, null without a camera. */
   private factor: number | null = null;
   /** Told the factor of every redraw: auto and fit change with the view. */
   onScaleShown: ((factor: number | null) => void) | null = null;
@@ -92,8 +92,9 @@ export class GameViewport extends WorldViewport {
 
   protected override currentView(): View | null {
     const camera = this.activeCamera();
-    this.factor = camera ? cameraFactor(camera.props, this.w, this.h, this.scaleMode) : null;
-    return camera ? cameraView(camera, this.w, this.h, this.scaleMode) : null;
+    const ratio = ui().app.renderer.resolution;
+    this.factor = camera ? cameraFactor(camera.props, this.w, this.h, this.scaleMode, ratio) : null;
+    return camera ? cameraView(camera, this.w, this.h, this.scaleMode, ratio) : null;
   }
 
   private activeCamera(): ActiveCamera | null {
@@ -106,8 +107,8 @@ export class GameViewport extends WorldViewport {
   }
 
   /**
-   * Screen pixels per camera pixel and per world unit, and the camera's picture as it lies on
-   * screen, in global pixels; null without a camera.
+   * Device pixels per camera pixel, CSS pixels per world unit, and the camera's picture as it
+   * lies on screen, in global CSS pixels; null without a camera.
    */
   scaleInfo(): {
     factor: number;