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/model/font.ts

@@ -1,4 +1,3 @@
-import type { FontAsset } from './Asset';
 import { findAsset, type Project } from './Project';
 
 /** Mirrors `FontStore::isValidName` on the server, where the name is derived from the bytes. */
@@ -23,7 +22,3 @@ export function fontFileOf(project: Project, id: string): string {
   const asset = findAsset(project, id);
   return asset?.type === 'font' ? asset.file : '';
 }
-
-export function isFontAsset(asset: { type: string }): asset is FontAsset {
-  return asset.type === 'font';
-}

src/core/model/sound.ts

@@ -1,4 +1,3 @@
-import type { SoundAsset } from './Asset';
 import { findAsset, type Project } from './Project';
 
 /** Mirrors `SoundStore::isValidName` on the server, where the name is derived from the bytes. */
@@ -14,7 +13,3 @@ export function soundFileOf(project: Project, id: string): string {
   const asset = findAsset(project, id);
   return asset?.type === 'sound' ? asset.file : '';
 }
-
-export function isSoundAsset(asset: { type: string }): asset is SoundAsset {
-  return asset.type === 'sound';
-}