Share the one HTTP envelope and the one byte formatter

Both stores carried their own ~28-line request<T>, and formatBytes existed
twice – the second copy had lost the "B" branch, so a small sprite would have
read as 0 KB had its caller ever passed one under a kilobyte.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/editor/textureImport.ts

@@ -2,6 +2,7 @@ import { CreateTextureCommand } from '../core/commands/assetCommands';
 import { nextAssetName } from '../core/commands/naming';
 import type { TextureAsset } from '../core/model/Asset';
 import type { TextureStore, UploadedTexture } from '../core/store/TextureStore';
+import { formatBytes } from '../ui';
 import type { EditorState } from './state';
 
 /** What the picker offers and a drop accepts; the server rejects everything else anyway. */
@@ -196,12 +197,6 @@ function assetNameFor(file: File): string {
   return file.name.replace(/\.[^.]+$/, '').trim() || 'Texture';
 }
 
-function formatBytes(bytes: number): string {
-  return bytes >= 1024 * 1024 ? `${(bytes / 1024 / 1024).toFixed(1)} MB` : `${Math.round(bytes / 1024)} KB`;
-}
-
-// --- ways in ---------------------------------------------------------------------------------
-
 /** Opens the browser's file dialog; resolves empty when the dialog was cancelled. */
 export function pickImageFiles(): Promise<File[]> {
   return new Promise((resolve) => {