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>

src/core/graph/nodes/index.ts

@@ -99,6 +99,7 @@ import { IndexOf } from './data/IndexOf';
 import { ItemAt } from './data/ItemAt';
 import { SetItem } from './data/SetItem';
 import { SubList } from './data/SubList';
+import { TextureSize } from './data/TextureSize';
 import { OnAnimationFinished } from './events/OnAnimationFinished';
 import { OnClick } from './events/OnClick';
 import { OnCollisionEnter } from './events/OnCollisionEnter';
@@ -184,6 +185,7 @@ export const BUILT_IN_NODES: readonly NodeDef[] = [
   IsEnabled,
   Properties,
   GetPosition,
+  TextureSize,
   NumberLiteral,
   BooleanLiteral,
   StringLiteral,