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/node-catalog.test.ts

@@ -265,6 +265,19 @@ const CASES: Record<string, Case[]> = {
       after: (ctx) => expect(ctx.states).toEqual({}),
     },
   ],
+  TextureSize: [
+    {
+      name: "hands out the picture's own pixel size",
+      inputs: { texture: 'coin' },
+      lookup: { ...NO_LOOKUP, textureSize: (id) => (id === 'coin' ? { w: 8, h: 6 } : null) },
+      outputs: { width: 8, height: 6 },
+    },
+    {
+      name: 'no picture is 0 × 0',
+      inputs: { texture: '' },
+      outputs: { width: 0, height: 0 },
+    },
+  ],
   CurrentState: [
     {
       name: 'names the state the machine is in, and hands out its id as well',