fix: add convenience fields to vendor product detail API response

Added title, description, image_url, and additional_images fields to
the product detail API response. These fields extract data from the
proper sources (translations, primary_image_url) for easier UI display.

Fixes image not displaying on product detail page (was using image_url
but API returned primary_image_url).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/services/vendor_product_service.py

@@ -192,6 +192,19 @@ class VendorProductService:
                 "description": t.description,
             }
 
+        # Convenience fields for UI (prefer vendor translations, fallback to English)
+        title = None
+        description = None
+        if vendor_translations:
+            # Try English first, then first available language
+            if "en" in vendor_translations:
+                title = vendor_translations["en"].get("title")
+                description = vendor_translations["en"].get("description")
+            elif vendor_translations:
+                first_lang = next(iter(vendor_translations))
+                title = vendor_translations[first_lang].get("title")
+                description = vendor_translations[first_lang].get("description")
+
         return {
             "id": product.id,
             "vendor_id": product.vendor_id,
@@ -233,6 +246,11 @@ class VendorProductService:
             # Translations
             "marketplace_translations": mp_translations,
             "vendor_translations": vendor_translations,
+            # Convenience fields for UI display
+            "title": title,
+            "description": description,
+            "image_url": product.primary_image_url,
+            "additional_images": product.additional_images or [],
             # Timestamps
             "created_at": product.created_at.isoformat()
             if product.created_at