Let a shader declare a color the sprite sets (#298)

A shader could only ask its sprites for numbers. A tint, an outline
colour or a glow colour had to be built from three Property nodes.

- New node Color property next to Property: Name and Default (a
  colour, white unless picked), output `color`. It becomes a colour
  row below the Shader dropdown and a vec3 uniform in the program.
- Number and colour properties share one set of names. A clash is
  the existing "Another property is named" problem.
- Like Color it cannot feed the Vertex output.
- Placed from the palette it is called tint, then tint2.
- The preview in the Shader tab shows a colour field for it. Like
  the sliders it starts at the sprite's value and never writes into
  the project.
- `declaredRows` takes the row builder, so the particle graph keeps
  its number rows unchanged.

Tests:
- Gate: 222 files, 3452 tests (3445 + 7)
- e2e 28: 89 checks (28l-v: default colour drawn, then the colour
  the sprite sets)
- e2e total 1704, counted (1703 + 1)

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

tools/e2e/28-shader.mjs

@@ -925,6 +925,29 @@ export async function shader(t) {
     { perCorner, perCornerReadout },
   );
 
+  // 28l-v. A Color property is a colour row on the sprite and a vec3 uniform (#298): unset, the
+  //        sprite shows the declared default; set on the sprite, that colour.
+  await graph(
+    [
+      node('tint', 'ShaderColorProperty', { name: 'tint', default: 0x3cc85a }),
+      node('out', 'ShaderOutput', {}, 780, 0),
+    ],
+    [edge('tint', 'color', 'out', 'color')],
+  );
+  const tinted = async () => ({ a: await pixel(-0.3, -0.3), b: await pixel(0.3, 0.3) });
+  const unsetTint = await tinted();
+  await assetProps({ tint: 0xe63c3c });
+  const setTint = await tinted();
+  check(
+    'a Color property draws its default, and the colour the sprite sets once it sets one',
+    colourDistance(unsetTint.a, '#3cc85a') < 12 &&
+      colourDistance(unsetTint.b, '#3cc85a') < 12 &&
+      colourDistance(setTint.a, '#e63c3c') < 12 &&
+      colourDistance(setTint.b, '#e63c3c') < 12,
+    { unsetTint, setTint },
+  );
+  await mutate(`delete __gm.state.project.assets.find((a) => a.id === 'shade-sprite').props.tint`);
+
   // 28l-ii. The sprite wears a picture and a shader: both open from the object's menu, from the
   //         asset's menu and from the inspector, whose Texture and Shader labels are links (#221).
   const shadedProps = await json("__gm.state.project.assets.find((a) => a.id === 'shade-sprite').props");