Drop the word image from the chat attachment alt (#133)

## Summary
- Closes #132.
- [Deploy Beta run 932](https://git.aimloperations.com/ai_ml_operations/chat_web_app/actions/runs/932/jobs/1572) failed `npm run build:beta` on ai-server-4080 because `CI=true` turns the `jsx-a11y/img-redundant-alt` warning into a compile error.
- The chat attachment `alt` is now `Attachment`, so the word `image` is gone. `CI=true` stays.

## Test plan
- [ ] ESLint on `ConversationDetailCard.tsx` reports no `img-redundant-alt` issue.
- [ ] After merge, deploy-beta on ai-server-4080 gets past `build:beta`.

Reviewed-on: #133

llm-fe/src/llm-fe/components/ConversationDetailCard/ConversationDetailCard.tsx

@@ -321,7 +321,7 @@ const ConversationDetailCard = ({
         {imageSrc && (
           <img
             src={imageSrc}
-            alt="Attached image"
+            alt="Attachment"
             style={{
               display: 'block',
               maxWidth: '100%',