Increase attached images limit to 4 images

app.py

@@ -272,8 +272,8 @@ async def generate_image(
     if image_urls:
         if not isinstance(image_urls, list):
             raise HTTPException(400, "image_urls must be a list")
-        if len(image_urls) > 2:
-            raise HTTPException(400, "Maximum of two image URLs allowed")
+        if len(image_urls) > 4:
+            raise HTTPException(400, "Maximum of four image URLs allowed")
         has_input_image = True
 
     if has_input_image: