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/core/store/HttpFileStore.ts

@@ -0,0 +1,31 @@
+import type { FileStore, StoredFile, UploadedFile } from './FileStore';
+import { apiRequest } from './http';
+
+/** The API's three file collections, one route each; textures, fonts and sounds differ in nothing else. */
+export type FileRoute = 'textures' | 'fonts' | 'sounds';
+
+export class HttpFileStore<
+  U extends UploadedFile = UploadedFile,
+  S extends StoredFile = StoredFile,
+> implements FileStore<U, S> {
+  constructor(
+    private readonly endpoint: string,
+    private readonly route: FileRoute,
+  ) {}
+
+  async upload(bytes: Blob | ArrayBuffer, type: string, name = ''): Promise<U> {
+    return apiRequest<U>(this.endpoint, 'POST', this.route, {
+      headers: { 'Content-Type': type },
+      body: bytes,
+      query: { name },
+    });
+  }
+
+  async list(): Promise<S[]> {
+    return apiRequest<S[]>(this.endpoint, 'GET', this.route, {});
+  }
+
+  async delete(file: string): Promise<void> {
+    await apiRequest<void>(this.endpoint, 'DELETE', `${this.route}/${encodeURIComponent(file)}`, {});
+  }
+}