fix(ui): P1-1 线程切换残留内容 + P2-5 列表项来源标注渲染

- main.tsx: 切换 threadId 时清空 lastMessagesRef，避免空对话显示上一条对话内容
- MessageBubble.tsx: li 元素增加 renderWithSourceBadges，[工单][知识库] 等标注在列表项中也渲染为彩色 badge

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

langgraph/src/components/MessageBubble.tsx

@@ -501,6 +501,20 @@ export default function MessageBubble({ content: rawContent, role, isStreaming,
             </ol>
           );
         },
+        li({ children }) {
+          const processedChildren = Array.isArray(children)
+            ? children.flatMap((child, idx) =>
+                typeof child === "string"
+                  ? renderWithSourceBadges(child).map((node, ni) =>
+                      typeof node === "string" ? node : <span key={`${idx}-${ni}`}>{node}</span>
+                    )
+                  : [child]
+              )
+            : typeof children === "string"
+              ? renderWithSourceBadges(children)
+              : children;
+          return <li>{processedChildren}</li>;
+        },
 
         // Paragraphs — inline source badges for [知识库] [工单] [网络] [推断]
         p({ children }) {

langgraph/src/main.tsx

@@ -154,6 +154,12 @@ function App() {
 
   // ── Active messages ──────────────────────────────────────────────────────
   const lastMessagesRef = useRef<Message[]>([]);
+  const lastThreadIdRef = useRef<string | null>(null);
+  // Clear stale messages when thread switches to avoid showing previous thread's content
+  if (currentThreadId !== lastThreadIdRef.current) {
+    lastMessagesRef.current = [];
+    lastThreadIdRef.current = currentThreadId;
+  }
   if (thread.messages.length > 0) {
     lastMessagesRef.current = thread.messages;
   }