Three stores, three importers and three pickers that differ only in their type are one of each (#85)

Refactoring round one: HttpFontStore/HttpSoundStore/HttpTextureStore collapse into a generic
HttpFileStore over a FileStore contract; fontImport/soundImport/textureImport share assetImport
with an ImportKind per sort; ImagePicker/FontPicker/SoundPicker sit on FilePicker and describe
only their row. The group/comment drag logic leaves GraphCanvas for annotationDrag.ts (with its
own unit test), declaredRows.ts replaces the duplicated row build in particles.ts and shaders.ts,
and dead code in font/sound/compile/emission/transform/actions is gone. README: asset list,
check count 958, the two-job CI, the Scenes wiki page.

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

src/viewport/ParticleLibrary.ts

@@ -1,5 +1,6 @@
 import type { ParticlesAsset } from '../core/model/Asset';
-import { compileParticles, type ParticlesBuild, particlesFingerprint } from '../core/particles/compile';
+import { graphFingerprint } from '../core/graph/Graph';
+import { compileParticles, type ParticlesBuild } from '../core/particles/compile';
 import { gameClock } from '../core/time';
 
 /**
@@ -22,12 +23,8 @@ export class ParticleLibrary {
     this.frozenAt = at;
   }
 
-  get frozen(): number | null {
-    return this.frozenAt;
-  }
-
   buildFor(asset: ParticlesAsset): ParticlesBuild {
-    const fingerprint = particlesFingerprint(asset.graph);
+    const fingerprint = graphFingerprint(asset.graph);
     const cached = this.builds.get(asset.id);
     if (cached && cached.fingerprint === fingerprint) return cached.build;
     this.compiles += 1;