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/FileStore.ts

@@ -0,0 +1,28 @@
+/**
+ * What the server answers for an upload: the content-addressed name it stored the bytes under
+ * (`{sha256}.{ext}`, see `isTextureFile`/`isFontFile`/`isSoundFile`) and the caption kept beside it.
+ */
+export interface UploadedFile {
+  file: string;
+  /** The name the file was uploaded under, '' when the server knows none. Never a path. */
+  name: string;
+  bytes: number;
+}
+
+/** A file the server holds, whether any project references it or not. */
+export interface StoredFile extends UploadedFile {
+  updatedAt: string;
+}
+
+/**
+ * Raw bytes rather than a multipart form: the server derives name and format from the file itself,
+ * so there is nothing else to send. `type` only fills the Content-Type header – the server trusts
+ * the bytes, not the label – and uploading the same bytes twice yields the same file, the hash of
+ * its content. `name` is the caption kept beside it; uploading the same bytes under a new name
+ * renames what the pickers show.
+ */
+export interface FileStore<U extends UploadedFile = UploadedFile, S extends StoredFile = StoredFile> {
+  upload(bytes: Blob | ArrayBuffer, type: string, name?: string): Promise<U>;
+  list(): Promise<S[]>;
+  delete(file: string): Promise<void>;
+}