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>

tests/core/shader-vertex.test.ts

@@ -83,7 +83,7 @@ describe('Vertex output (#79)', () => {
     s.link(amount, 'value', s.corner, 'y');
     s.link(amount, 'value', s.out, 'alpha');
     const { compiled } = s.build();
-    expect(compiled!.uniforms).toEqual([{ name: 'amount', default: 1 }]);
+    expect(compiled!.uniforms).toEqual([{ name: 'amount', kind: 'number', default: 1 }]);
     expect(compiled!.fragment).toContain('float n0_value = u_amount;');
     expect(compiled!.vertex!.body).toContain('float c0_value = u_amount;');
     // One precision for a uniform both stages declare: the fragment's default.