A particle is a function of its age, not a thing that is stepped (#73)

The asset type `particles` is placeable and carries a graph at the same time —
`behavior` was the blueprint. Because a continuous emitter gives birth to particle n
at time n/rate, the whole field is a function of the clock rather than of the frames:
no ring-buffer bookkeeping, exact time jumps, reproducibility as a measurable property.

compile.ts follows compileShader's frame but emits JS closures into a Float64Array
instead of GLSL, and without eval; a node with two consumers is evaluated once.
Drawing is one Pixi ParticleContainer per source, so one draw call.

Collision, wind and braking in flight are out for good — that is the price of the
formula model, not an omission.

The tab count goes from nine to ten, which is exactly the case #84 was built for one
day earlier: at 1280 px the row no longer holds every tab, so guard 14b now asks for
hidden.length > 0 instead of === 0.

src/editor/graph/GraphCanvas.ts

@@ -28,6 +28,7 @@ import {
 } from '../../core/graph';
 import type { GraphAsset } from '../../core/model/Asset';
 import { graphLookup } from '../../core/model/graphLookup';
+import { particleLibrary } from '../../viewport/ParticleLibrary';
 import { shaderLibrary } from '../../viewport/ShaderLibrary';
 import { findAsset, findGraphAsset } from '../../core/model/Project';
 import { type Trace, TRACE_FADE } from '../../runtime/systems/BehaviorSystem';
@@ -219,8 +220,13 @@ export class GraphCanvas extends Widget {
     }
     const seen = new Set<string>();
     const lookup = graphLookup(this.state.project);
-    // A shader node's problem is the compiler's, not a call's.
-    const shaderProblems = asset.type === 'shader' ? shaderLibrary.buildFor(asset).problems : null;
+    // In a compiled graph a node's problem is the compiler's, not a call's.
+    const compilerProblems =
+      asset.type === 'shader'
+        ? shaderLibrary.buildFor(asset).problems
+        : asset.type === 'particles'
+          ? particleLibrary.buildFor(asset).problems
+          : null;
     for (const node of asset.graph.nodes) {
       const def = resolveDef(node, asset.graph, lookup);
       if (!def) continue;
@@ -233,8 +239,8 @@ export class GraphCanvas extends Widget {
         this.views.set(node.id, view);
         this.nodeLayer.addChild(view);
       }
-      const problem = shaderProblems
-        ? (shaderProblems[node.id] ?? null)
+      const problem = compilerProblems
+        ? (compilerProblems[node.id] ?? null)
         : callProblem(node, lookup, asset.id);
       view.sync(node, asset.graph, this.state.project, def, problem);
     }