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>

src/core/shader/nodes.ts

@@ -2,9 +2,15 @@ import type { PortType } from '../graph/Graph';
 import type { NodeDef, PortDef } from '../graph/NodeRegistry';
 import type { SharedPortGroup } from '../graph/portTypes';
 import { type PropertyBag, textOf } from '../model/Properties';
-import { propertyNodeParams } from '../properties/declaredRows';
+import { PROPERTY_DEFAULT_PARAM, propertyNodeParams } from '../properties/declaredRows';
 import { flatDef } from '../properties/PropertySchema';
-import { PROPERTY_NAME_PARAM, propertyName, SHADER_PROPERTY } from '../properties/shaders';
+import {
+  DEFAULT_PROPERTY_COLOR,
+  PROPERTY_NAME_PARAM,
+  propertyName,
+  SHADER_COLOR_PROPERTY,
+  SHADER_PROPERTY,
+} from '../properties/shaders';
 
 export type GlslType = 'float' | 'vec3';
 
@@ -341,6 +347,25 @@ export const ShaderProperty: ShaderNodeDef = {
   }),
 };
 
+/** The same for a colour (#298); like `Color`, there is none per corner. */
+export const ShaderColorProperty: ShaderNodeDef = {
+  type: SHADER_COLOR_PROPERTY,
+  label: 'Color property',
+  category: 'shader',
+  description: 'A color the sprite sets: a color row below the Shader dropdown, and a color here.',
+  inputs: [],
+  outputs: [vec3Port('color')],
+  params: [
+    flatDef(PROPERTY_NAME_PARAM, 'text', { label: 'Name', value: 'value' }),
+    flatDef(PROPERTY_DEFAULT_PARAM, 'color', { label: 'Default', value: DEFAULT_PROPERTY_COLOR }),
+  ],
+  perPixel: true,
+  derivePorts: ({ node }) => ({ label: propertyName(node) || ShaderColorProperty.label }),
+  emit: (_inputs, params) => ({
+    color: { code: uniformName(textOf(params[PROPERTY_NAME_PARAM] ?? '')), type: 'vec3' },
+  }),
+};
+
 export function uniformName(property: string): string {
   return `u_${property}`;
 }
@@ -550,6 +575,7 @@ export const SHADER_NODES: readonly ShaderNodeDef[] = [
   ShaderOutput,
   ShaderVertexOutput,
   ShaderProperty,
+  ShaderColorProperty,
   ShaderColor,
   ShaderNumber,
   ShaderAdd,