feat(14-02): add clickable attachment links with signed URL fetching

- Import getMusicNotationUrl REST helper and useState/useCallback hooks
- Add handleAttachmentClick handler that fetches signed S3 URL and opens in new tab
- Implement loading state (isLoadingUrl) to prevent rapid clicks
- Make filename a clickable link with underline and blue color
- Add error handling that logs to console without crashing
- Show 'wait' cursor during URL fetch
- Browser handles file display based on Content-Type (PDF viewer, image display, audio player)

jam-ui/src/components/client/chat/JKChatMessage.js

@@ -1,7 +1,8 @@
-import React from 'react';
+import React, { useCallback, useState } from 'react';
 import PropTypes from 'prop-types';
 import { formatTimestamp } from '../../../utils/formatTimestamp';
 import { formatFileSize } from '../../../services/attachmentValidation';
+import { getMusicNotationUrl } from '../../../helpers/rest';
 
 /**
  * Get initials for avatar from sender name
@@ -40,7 +41,35 @@ const isAttachmentMessage = message => {
  * - React.memo for performance optimization
  */
 const JKChatMessage = ({ message }) => {
-  const { senderName, message: text, createdAt, attachmentName, attachmentSize } = message;
+  const { senderName, message: text, createdAt, attachmentId, attachmentName, attachmentSize } = message;
+  const [isLoadingUrl, setIsLoadingUrl] = useState(false);
+
+  /**
+   * Handle attachment click - fetch signed S3 URL and open in new tab
+   * @param {string} attachmentId - ID of the attachment to open
+   */
+  const handleAttachmentClick = useCallback(
+    async attachmentId => {
+      if (isLoadingUrl) return; // Prevent rapid clicks
+
+      try {
+        setIsLoadingUrl(true);
+        const response = await getMusicNotationUrl(attachmentId);
+        // Response is { url: "https://s3.amazonaws.com/...?signature=..." }
+        if (response && response.url) {
+          window.open(response.url, '_blank');
+        } else {
+          console.error('No URL in response:', response);
+        }
+      } catch (error) {
+        console.error('Failed to fetch attachment URL:', error);
+        // Could show toast error here, but keep it simple for now
+      } finally {
+        setIsLoadingUrl(false);
+      }
+    },
+    [isLoadingUrl]
+  );
 
   // Common avatar style
   const avatarStyle = {
@@ -85,16 +114,41 @@ const JKChatMessage = ({ message }) => {
             <span style={{ fontWeight: 600, fontSize: '14px', color: '#212529' }}>{senderName || 'Unknown'}</span>
             <span style={{ fontSize: '12px', color: '#6c757d' }}>{formatTimestamp(createdAt)}</span>
           </div>
-          <div style={{ fontSize: '14px', color: '#212529', display: 'flex', alignItems: 'center' }}>
+          <div
+            style={{
+              fontSize: '14px',
+              color: '#212529',
+              display: 'flex',
+              alignItems: 'center',
+              flexWrap: 'wrap',
+              gap: '4px'
+            }}
+          >
             <span style={fileIconStyle} role="img" aria-label="attachment">
               📎
             </span>
-            <span>
-              attached <strong>{attachmentName}</strong>
-              {attachmentSize && (
-                <span style={{ color: '#6c757d', marginLeft: '4px' }}>({formatFileSize(attachmentSize)})</span>
-              )}
+            <span>attached</span>
+            <span
+              onClick={() => handleAttachmentClick(attachmentId)}
+              style={{
+                cursor: isLoadingUrl ? 'wait' : 'pointer',
+                color: '#1976d2',
+                textDecoration: 'underline',
+                fontWeight: 600,
+                maxWidth: '200px',
+                overflow: 'hidden',
+                textOverflow: 'ellipsis',
+                whiteSpace: 'nowrap',
+                display: 'inline-block',
+                verticalAlign: 'bottom'
+              }}
+              title={attachmentName}
+            >
+              {attachmentName}
             </span>
+            {attachmentSize && (
+              <span style={{ color: '#6c757d', flexShrink: 0 }}>({formatFileSize(attachmentSize)})</span>
+            )}
           </div>
         </div>
       </div>