Clean up presigned URL implementation: remove dead fields, fix error handling

- Remove unused image_url from upload response and TS type
- Remove bare except in serve_image that masked config errors as 404s
- Add error state and broken-image placeholder in QuestionBubble

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

raggr-frontend/src/api/conversationService.ts

@@ -125,7 +125,7 @@ class ConversationService {
   async uploadImage(
     file: File,
     conversationId: string,
-  ): Promise<{ image_key: string; image_url: string }> {
+  ): Promise<{ image_key: string }> {
     const formData = new FormData();
     formData.append("file", file);
     formData.append("conversation_id", conversationId);

raggr-frontend/src/components/QuestionBubble.tsx

@@ -9,10 +9,17 @@ type QuestionBubbleProps = {
 
 export const QuestionBubble = ({ text, image_key }: QuestionBubbleProps) => {
   const [imageUrl, setImageUrl] = useState<string | null>(null);
+  const [imageError, setImageError] = useState(false);
 
   useEffect(() => {
     if (!image_key) return;
-    conversationService.getPresignedImageUrl(image_key).then(setImageUrl).catch(() => {});
+    conversationService
+      .getPresignedImageUrl(image_key)
+      .then(setImageUrl)
+      .catch((err) => {
+        console.error("Failed to load image:", err);
+        setImageError(true);
+      });
   }, [image_key]);
 
   return (
@@ -25,6 +32,12 @@ export const QuestionBubble = ({ text, image_key }: QuestionBubbleProps) => {
           "shadow-sm shadow-leaf/10",
         )}
       >
+        {imageError && (
+          <div className="flex items-center gap-2 text-xs text-charcoal/50 bg-charcoal/5 rounded-xl px-3 py-2 mb-2">
+            <span>🖼️</span>
+            <span>Image failed to load</span>
+          </div>
+        )}
         {imageUrl && (
           <img
             src={imageUrl}