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/core/store/HttpTextureStore.ts

@@ -1,7 +1,6 @@
-import { statusMessage } from './http';
+import { apiRequest } from './http';
 import type { StoredTexture, TextureStore, UploadedTexture } from './TextureStore';
 
-/** Routing goes through the `r` query parameter because nginx does not pass PATH_INFO to PHP. */
 export class HttpTextureStore implements TextureStore {
   constructor(private readonly endpoint: string) {}
 
@@ -22,28 +21,9 @@ export class HttpTextureStore implements TextureStore {
     route: string,
     payload?: { bytes: Blob | ArrayBuffer; type: string },
   ): Promise<T> {
-    const url = `${this.endpoint}?r=${encodeURIComponent(route)}`;
-    const response = await fetch(url, {
-      method,
+    return apiRequest<T>(this.endpoint, method, route, {
       headers: payload ? { 'Content-Type': payload.type } : {},
       body: payload?.bytes,
     });
-    if (response.status === 204) return undefined as T;
-    const text = await response.text();
-    let data: unknown;
-    try {
-      data = text ? JSON.parse(text) : null;
-    } catch {
-      // An upload is the request nginx refuses before PHP sees it, answering with an HTML page,
-      // so a failure is explained from the status instead.
-      if (response.ok) throw new Error(`API ${method} ${route}: invalid JSON (${response.status})`);
-      data = null;
-    }
-    if (!response.ok) {
-      const message =
-        (data as { error?: string } | null)?.error ?? statusMessage(response.status, response.statusText);
-      throw new Error(`API ${method} ${route}: ${message} (${response.status})`);
-    }
-    return data as T;
   }
 }