batch3 T8 review fix: preserve cloneElement key in linkifyChildren

cloneElement does not carry el.key through unless explicitly passed.
Without it, react-markdown's inline-element siblings (strong/em/text)
lose their reconciler keys on every render, causing potential diffing
churn. Pass el.key (with fallback) explicitly.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/web/src/components/MessageBubble.tsx

@@ -74,6 +74,7 @@ function linkifyChildren(children: ReactNode, keyPrefix = 'l'): ReactNode {
       const grandchildren = el.props.children;
       if (grandchildren === undefined) return child;
       return cloneElement(el, {
+        key: el.key ?? `linkified-${i}`,
         children: linkifyChildren(grandchildren, `${keyPrefix}-${i}`),
       });
     }