Shader assets: graph-built shaders, the Shader tab and sprite rows from the graph (#62)

A shader is an asset carrying a node graph (Texture color, Output, Property,
Color, Add/Subtract/Multiply/Divide, Mix, Luminance) that compiles to the GLSL
fragment of a Pixi filter. The Shader tab reuses the Behavior canvas; a sprite
wears a shader through its Shader picker, and the rows below it are the
graph's Property nodes. Property schema, resolution and deviation take the
project because a sprite's rows now live in another asset. The built-in
registry of the prototype is gone; "Adjust colors" ships as a graph in the
fixture and the three example games.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

src/core/graph/nodes/index.ts

@@ -88,6 +88,7 @@ import { RunBehavior } from './flow/RunBehavior';
 import { Sequence } from './flow/Sequence';
 import { SetState } from './flow/SetState';
 import { StateBranch } from './flow/StateBranch';
+import { SHADER_NODES } from '../../shader/nodes';
 import { State } from '../stateMachine';
 import { Variables } from './variable/Variables';
 
@@ -187,5 +188,7 @@ export const BUILT_IN_NODES: readonly NodeDef[] = [
 ];
 
 for (const def of BUILT_IN_NODES) registerNode(def);
-// Registered so a machine's graph loads and draws, but not built in: no behavior graph offers it.
+// Registered so a machine's or a shader's graph loads and draws, but not built in: no behavior
+// graph offers them.
 registerNode(State);
+for (const def of SHADER_NODES) registerNode(def);