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/core/model/Asset.ts

@@ -110,6 +110,16 @@ export interface FontAsset extends AssetBase {
   file: string;
 }
 
+/**
+ * The graph is the motion of one particle: every output of its `Output` node is a function of the
+ * particle's age and its own random number (see `core/particles/compile.ts`). A placed object is
+ * the source that emits them; how many and for how long are its properties.
+ */
+export interface ParticlesAsset extends AssetBase {
+  type: 'particles';
+  graph: Graph;
+}
+
 export type Asset =
   | SpriteAsset
   | CameraAsset
@@ -122,13 +132,16 @@ export type Asset =
   | AnimationAsset
   | StateMachineAsset
   | ShaderAsset
-  | FontAsset;
+  | FontAsset
+  | ParticlesAsset;
 
 /** The assets edited as a node graph – what the graph canvas and the graph commands work on. */
-export type GraphAsset = BehaviorAsset | StateMachineAsset | ShaderAsset;
+export type GraphAsset = BehaviorAsset | StateMachineAsset | ShaderAsset | ParticlesAsset;
+
+const GRAPH_TYPES: ReadonlySet<AssetType> = new Set(['behavior', 'statemachine', 'shader', 'particles']);
 
 export function isGraphAsset(asset: Asset): asset is GraphAsset {
-  return asset.type === 'behavior' || asset.type === 'statemachine' || asset.type === 'shader';
+  return GRAPH_TYPES.has(asset.type);
 }
 
 export function isSceneAsset(asset: Asset): asset is SceneAsset {

src/core/model/AssetTypes.ts

@@ -11,6 +11,7 @@ export const ASSET_TYPES = [
   'statemachine',
   'shader',
   'font',
+  'particles',
 ] as const;
 
 export type AssetType = (typeof ASSET_TYPES)[number];
@@ -28,6 +29,7 @@ export const ASSET_TYPE_LABELS: Record<AssetType, string> = {
   statemachine: 'State machine',
   shader: 'Shader',
   font: 'Font',
+  particles: 'Particles',
 };
 
 /**