🐛 fix(playground): ensure proper streaming updates & safeguard message handling

Summary
This commit addresses two critical issues affecting the real-time chat experience in the Playground:

1. Optimized re-rendering of reasoning content
   • Added `reasoningContent` to the comparison function of `OptimizedMessageContent` (`web/src/components/playground/OptimizedComponents.js`).
   • Ensures the component re-renders while reasoning text streams, resolving the bug where only the first characters (“好,”) were shown until the stream finished.

2. Defensive checks for SSE message updates
   • Added early-return guards in `streamMessageUpdate` (`web/src/hooks/useApiRequest.js`).
   • Skips updates when `lastMessage` is undefined or the last message isn’t from the assistant, preventing `TypeError: Cannot read properties of undefined (reading 'status')` during rapid SSE responses.

Impact
• Real-time reasoning content now appears progressively, enhancing user feedback.
• Eliminates runtime crashes caused by undefined message references, improving overall stability.

web/src/hooks/useApiRequest.js

@@ -38,6 +38,8 @@ export const useApiRequest = (
   const streamMessageUpdate = useCallback((textChunk, type) => {
     setMessage(prevMessage => {
       const lastMessage = prevMessage[prevMessage.length - 1];
+      if (!lastMessage) return prevMessage;
+      if (lastMessage.role !== 'assistant') return prevMessage;
       if (lastMessage.status === MESSAGE_STATUS.ERROR) {
         return prevMessage;
       }