Read the pixel size of a texture in a graph (#262)

A graph had no way to know how big a picture is. An icon sprite with a
fixed size therefore stretched every icon of another size, an 8x8
pixel-art icon in a 16x16 slot was drawn twice as big.

- New data node Texture size. It takes a texture, a frame or a pixel
  art and hands out width and height in pixels, 0 x 0 for none.
  Wired into a sprite's width and height, the picture shows pixel for
  pixel.
- GraphLookup gets textureSize. The project answers it with the same
  pictureSize rule a sprite uses to size itself.

Tests:

- ./check.sh: 2749 tests, CHECK EXIT 0.
- 2 catalog cases (a picture, no picture) and one test against a real
  project: pixel-art sheet, single frame, missing texture.
- No e2e check and no counter-check for this node.

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

tests/core/pixel-art.test.ts

@@ -54,6 +54,7 @@ import {
   withLayerMoved,
   withLayerRemoved,
 } from '../../src/core/model/pixelEdit';
+import { graphLookup } from '../../src/core/model/graphLookup';
 import { findAsset, type Project } from '../../src/core/model/Project';
 import { resolvePicture } from '../../src/core/model/texture';
 import { pictureChoices, textureRefLabel } from '../../src/core/properties/textureRef';
@@ -295,6 +296,23 @@ describe('the picture', () => {
     }
   });
 
+  it('tells a graph its own pixel size, the sheet for the asset and the cut for a frame', () => {
+    const remove = registerPictureSource('pixelart', pixelArtPicture);
+    try {
+      const { project } = makeProject();
+      const asset = art(project);
+      asset.width = 8;
+      asset.height = 6;
+      asset.frames.push({ id: 'second', cels: {} });
+      const lookup = graphLookup(project);
+      expect(lookup.textureSize(asset.id)).toEqual({ w: 16, h: 6 });
+      expect(lookup.textureSize('second')).toEqual({ w: 8, h: 6 });
+      expect(lookup.textureSize('gone')).toBeNull();
+    } finally {
+      remove();
+    }
+  });
+
   it('with one frame is offered as the picture alone', () => {
     const remove = registerPictureSource('pixelart', pixelArtPicture);
     try {