Add copy button to assistant messages

components/MessageList.tsx

@@ -60,11 +60,39 @@ export default function MessageList() {
               <span style={{ whiteSpace: 'pre-wrap' }}>{m.content}</span>
             )}
           </div>
-          {m.sources && m.sources.length > 0 && (
-            <div className="text-xs mt-1.5 italic" style={{ color: 'var(--text3)' }}>
-              Sources: {[...new Set(m.sources)].join(', ')}
-            </div>
-          )}
+          <div className="flex items-center gap-2 mt-1.5">
+            {m.role === 'assistant' && (
+              <button
+                onPointerUp={() => {
+                  navigator.clipboard.writeText(m.content);
+                }}
+                style={{
+                  background: 'none',
+                  border: 'none',
+                  cursor: 'pointer',
+                  padding: '2px 6px',
+                  borderRadius: '4px',
+                  color: 'var(--text3)',
+                  fontSize: '11px',
+                  display: 'flex',
+                  alignItems: 'center',
+                  gap: '4px',
+                }}
+                title="Copy response"
+              >
+                <svg width="12" height="12" viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2">
+                  <rect x="9" y="9" width="13" height="13" rx="2" ry="2"/>
+                  <path d="M5 15H4a2 2 0 0 1-2-2V4a2 2 0 0 1 2-2h9a2 2 0 0 1 2 2v1"/>
+                </svg>
+                Copy
+              </button>
+            )}
+            {m.sources && m.sources.length > 0 && (
+              <div className="text-xs italic" style={{ color: 'var(--text3)' }}>
+                Sources: {[...new Set(m.sources)].join(', ')}
+              </div>
+            )}
+          </div>
         </div>
       ))}