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>

tests/editor/font-import.test.ts

@@ -8,7 +8,7 @@ import { createEmptyProject } from '../../src/core/model/Project';
 import type { FontStore } from '../../src/core/store/FontStore';
 import { importFonts, importStoredFont, isFontFileName } from '../../src/editor/fontImport';
 import { EditorState } from '../../src/editor/state';
-import { importNotice } from '../../src/editor/textureImport';
+import { importNotice } from '../../src/editor/assetImport';
 
 const FILE = `${'a'.repeat(64)}.ttf`;
 const font = { file: FILE, name: '', bytes: 380_660 };