feat(ecommerce): use FormData binary upload instead of base64 dataUrl

- Add uploadAssetBinary method to aiGenerationClient (FormData + busboy)
- Replace base64 dataUrl upload in uploadProductImages with direct blob upload
  via /oss/upload-binary multipart endpoint
- This eliminates the DATA_URL_PATTERN regex parsing bug that produced
  44-byte corrupt files on OSS, causing DashScope "image format illegal" errors

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/api/aiGenerationClient.ts

@@ -403,6 +403,22 @@ export const aiGenerationClient = {
     return readJsonResponse<{ url: string; ossKey?: string }>(res, "Asset upload response failed");
   },
 
+  async uploadAssetBinary(blob: Blob, options?: { name?: string; mimeType?: string; scope?: string }): Promise<{ url: string; signedUrl?: string; ossKey?: string }> {
+    const form = new FormData();
+    form.append("file", blob, options?.name || "upload.png");
+    if (options?.scope) form.append("scope", options.scope);
+    if (options?.mimeType) form.append("mimeType", options.mimeType);
+    const res = await fetch(buildApiUrl("oss/upload-binary"), {
+      method: "POST",
+      headers: { ...buildAuthHeaders() },
+      body: form,
+    });
+    if (!res.ok) {
+      await throwResponseError(res, "Binary asset upload failed");
+    }
+    return readJsonResponse<{ url: string; ossKey?: string }>(res, "Binary asset upload response failed");
+  },
+
   async uploadAssetByUrl(input: UploadAssetByUrlInput): Promise<{ url: string; signedUrl?: string; ossKey?: string }> {
     const res = await fetch(buildApiUrl("oss/upload-by-url"), {
       method: "POST",