Shader graph: UV, Sample texture, Texture size, Time, Sin/Floor/Fract/Step; edge mode on Output (#78)

Fragment-side coordinate nodes instead of vertex nodes: the quad stays the
quad, a UV read plus a sample at a computed coordinate covers flip, scroll,
wave, pixelate and scanlines. Time is a uniform only when a Time node reaches
the Output; a viewport that drew a Time shader redraws from the ticker so the
Scene tab animates without a running world. Edge (Mirror/Repeat/Clamp) is a
second texture variant in TextureLibrary because WebGL binds no TextureStyle
resource of the shader. The compiler now emits #version 300 es first: Pixi
only compiles as ES 3.00 when the fragment says so, and textureSize needs it.

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

src/viewport/ShaderLibrary.ts

@@ -9,6 +9,18 @@ import type { ShaderSource } from './shaders';
  */
 export class ShaderLibrary {
   private readonly builds = new Map<string, { fingerprint: string; build: ShaderBuild }>();
+  private readonly started = performance.now();
+  /** Set from the test hook: the clock stands at this second until released. */
+  private frozenAt: number | null = null;
+
+  /** Seconds since the library came up – what a Time node reads. */
+  now(): number {
+    return this.frozenAt ?? (performance.now() - this.started) / 1000;
+  }
+
+  freezeTime(at: number | null): void {
+    this.frozenAt = at;
+  }
 
   buildFor(asset: ShaderAsset): ShaderBuild {
     const fingerprint = JSON.stringify(asset.graph);
@@ -23,6 +35,7 @@ export class ShaderLibrary {
   source(project: Project): ShaderSource {
     const seen = new Map<string, ShaderBuild | null>();
     return {
+      now: this.now(),
       compiled: (assetId) => {
         let build = seen.get(assetId);
         if (build === undefined) {