Create a sprite asset from a texture's context menu

The sprite takes the whole image at its pixel size and the texture's name,
numbered like any other clash. CreateAssetCommand now accepts starting
properties; they go through the schema in execute, so an unknown key or a
bad value is refused before the project is touched, and one undo removes
the asset.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/core/properties/aspect.ts

@@ -22,6 +22,13 @@ export function texturePixelSize(project: Project, props: PropertyBag): PixelSiz
   return w > 0 && h > 0 ? { w, h } : null;
 }
 
+/** A sprite wearing the texture at its own pixel size – or at the default size while that is unknown. */
+export function spriteFromTexture(project: Project, textureId: string): PropertyBag {
+  const props: PropertyBag = { texture: textureId };
+  const size = texturePixelSize(project, props);
+  return size ? { ...props, width: size.w, height: size.h } : props;
+}
+
 /**
  * What `axis` has to become for the sprite to carry the picture's proportions, leaving the
  * other side where it is. Null when the other side is not a usable number.