🔧 fix(playground): resolve message state issues after page refresh and config reset

**Problem 1: Chat interface not refreshing when resetting imported messages**
- The "reset messages simultaneously" option during config import failed to
  update the chat interface properly
- Normal conversation resets worked correctly

**Problem 2: Messages stuck in loading state after page refresh**
- When AI was generating a response and user refreshed the page, the message
  remained in loading state indefinitely
- Stop button had no effect on these orphaned loading messages

**Changes Made:**

1. **Fixed config reset message refresh** (`usePlaygroundState.js`):
   ```javascript
   // Clear messages first, then set defaults to force component re-render
   setMessage([]);
   setTimeout(() => {
     setMessage(DEFAULT_MESSAGES);
   }, 0);
   ```

2. **Enhanced stop generator functionality** (`useApiRequest.js`):
   ```javascript
   // Handle orphaned loading messages even without active SSE connection
   const onStopGenerator = useCallback(() => {
     // Close active SSE if exists
     if (sseSourceRef.current) {
       sseSourceRef.current.close();
       sseSourceRef.current = null;
     }

     // Always attempt to complete any loading/incomplete messages
     // ... processing logic
   }, [setMessage, applyAutoCollapseLogic, saveMessages]);
   ```

3. **Added automatic message state recovery** (`usePlaygroundState.js`):
   ```javascript
   // Auto-fix loading/incomplete messages on page load
   useEffect(() => {
     const lastMsg = message[message.length - 1];
     if (lastMsg.status === MESSAGE_STATUS.LOADING ||
         lastMsg.status === MESSAGE_STATUS.INCOMPLETE) {
       // Process incomplete content and mark as complete
       // Save corrected message state
     }
   }, []);
   ```

**Root Cause:**
- Config reset: Direct state assignment didn't trigger component refresh
- Loading state: No recovery mechanism for interrupted SSE connections after refresh

**Impact:**
- ✅ Config reset now properly refreshes chat interface
- ✅ Stop button works on orphaned loading messages
- ✅ Page refresh automatically recovers incomplete messages
- ✅ No more permanently stuck loading states

web/src/hooks/useApiRequest.js

@@ -348,41 +348,45 @@ export const useApiRequest = (
 
   // 停止生成
   const onStopGenerator = useCallback(() => {
+    // 如果仍有活动的 SSE 连接，首先关闭
     if (sseSourceRef.current) {
       sseSourceRef.current.close();
       sseSourceRef.current = null;
-
-      setMessage(prevMessage => {
-        const lastMessage = prevMessage[prevMessage.length - 1];
-        if (lastMessage.status === MESSAGE_STATUS.LOADING ||
-          lastMessage.status === MESSAGE_STATUS.INCOMPLETE) {
-
-          const processed = processIncompleteThinkTags(
-            lastMessage.content || '',
-            lastMessage.reasoningContent || ''
-          );
-
-          const autoCollapseState = applyAutoCollapseLogic(lastMessage, true);
-
-          const updatedMessages = [
-            ...prevMessage.slice(0, -1),
-            {
-              ...lastMessage,
-              status: MESSAGE_STATUS.COMPLETE,
-              reasoningContent: processed.reasoningContent || null,
-              content: processed.content,
-              ...autoCollapseState,
-            }
-          ];
-
-          // 停止生成时也保存，传入更新后的消息列表
-          setTimeout(() => saveMessages(updatedMessages), 0);
-
-          return updatedMessages;
-        }
-        return prevMessage;
-      });
     }
+
+    // 无论是否存在 SSE 连接，都尝试处理最后一条正在生成的消息
+    setMessage(prevMessage => {
+      if (prevMessage.length === 0) return prevMessage;
+      const lastMessage = prevMessage[prevMessage.length - 1];
+
+      if (lastMessage.status === MESSAGE_STATUS.LOADING ||
+        lastMessage.status === MESSAGE_STATUS.INCOMPLETE) {
+
+        const processed = processIncompleteThinkTags(
+          lastMessage.content || '',
+          lastMessage.reasoningContent || ''
+        );
+
+        const autoCollapseState = applyAutoCollapseLogic(lastMessage, true);
+
+        const updatedMessages = [
+          ...prevMessage.slice(0, -1),
+          {
+            ...lastMessage,
+            status: MESSAGE_STATUS.COMPLETE,
+            reasoningContent: processed.reasoningContent || null,
+            content: processed.content,
+            ...autoCollapseState,
+          }
+        ];
+
+        // 停止生成时也保存，传入更新后的消息列表
+        setTimeout(() => saveMessages(updatedMessages), 0);
+
+        return updatedMessages;
+      }
+      return prevMessage;
+    });
   }, [setMessage, applyAutoCollapseLogic, saveMessages]);
 
   // 发送请求