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/editor/App.ts

@@ -1,8 +1,7 @@
 import type { Application } from 'pixi.js';
-import { HttpFontStore } from '../core/store/HttpFontStore';
+import { HttpFileStore } from '../core/store/HttpFileStore';
 import { HttpProjectStore } from '../core/store/HttpProjectStore';
-import { HttpSoundStore } from '../core/store/HttpSoundStore';
-import { HttpTextureStore } from '../core/store/HttpTextureStore';
+import type { StoredTexture, UploadedTexture } from '../core/store/TextureStore';
 import { requestRender, type VStack } from '../ui';
 import { fontLibrary } from '../viewport/FontLibrary';
 import { soundLibrary } from '../viewport/SoundLibrary';
@@ -32,9 +31,9 @@ export async function startEditor(app: Application, root: VStack): Promise<void>
     root,
     state,
     new HttpProjectStore(API_ENDPOINT),
-    new HttpTextureStore(API_ENDPOINT),
-    new HttpFontStore(API_ENDPOINT),
-    new HttpSoundStore(API_ENDPOINT),
+    new HttpFileStore<UploadedTexture, StoredTexture>(API_ENDPOINT, 'textures'),
+    new HttpFileStore(API_ENDPOINT, 'fonts'),
+    new HttpFileStore(API_ENDPOINT, 'sounds'),
   );
   // An image or a font arrives long after the click that asked for it, and the widget waiting for
   // it repaints without telling anyone: both libraries are a wake-up of their own.