fix(ecommerce): 502 bug - vision model upgrade + MIME normalization + fallback

- Upgrade VISION_MODEL to qwen3.7-plus (latest, confirmed working with image_url)
- Add VISION_FALLBACK_MODEL = qwen-vl-plus for retry on "image format" errors
- Normalize upload MIME types: unsupported formats (HEIC/AVIF) fall back to image/png
  to prevent server saving as .bin which DashScope can't read
- Server-side: add image/avif, image/heic, image/heif to MIME_EXTENSIONS

Root cause: DashScope returned "image format is illegal" when uploaded images
had unrecognized MIME types → saved as .bin → DashScope couldn't decode.

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

src/features/ecommerce/EcommercePage.tsx

@@ -1321,18 +1321,20 @@ function ProductClonePage(_props: ProductClonePageProps = {}) {
   });
 
   const uploadProductImages = async (): Promise<string[]> => {
+    const SUPPORTED_IMAGE_TYPES = new Set(["image/jpeg", "image/png", "image/webp", "image/gif"]);
     const urls: string[] = [];
     for (const item of productImages) {
       try {
         const resp = await fetch(item.src);
         const blob = await resp.blob();
+        const mimeType = SUPPORTED_IMAGE_TYPES.has(blob.type) ? blob.type : "image/png";
         const dataUrl = await new Promise<string>((resolve, reject) => {
           const reader = new FileReader();
           reader.onload = () => resolve(String(reader.result));
           reader.onerror = () => reject(reader.error);
           reader.readAsDataURL(blob);
         });
-        const { url } = await aiGenerationClient.uploadAsset({ dataUrl, name: item.name, mimeType: blob.type });
+        const { url } = await aiGenerationClient.uploadAsset({ dataUrl, name: item.name, mimeType });
         urls.push(url);
       } catch {
         // skip images that fail to upload