fix(chat): 修复重连后对话状态丢失导致消息发送失败的问题

在 WebSocket 重连场景下，服务端可能丢失 `conversationId` 状态，导致后续消息发送被拒绝。通过在客户端消息中携带 `conversationId`，并在服务端添加 fallback 恢复逻辑，确保重连后仍能正常发送消息。

同时优化了 `pendingMessage` 类型定义，支持存储待发送的图片附件，修复了延迟发送场景下图片丢失的问题。

web/client/src/components/chat/ChatView.tsx

@@ -19,7 +19,7 @@ export function ChatView() {
   const [manifestPath, setManifestPath] = useState<string | null>(null);
   const [accounts, setAccounts] = useState<Account[]>([]);
   const [quote, setQuote] = useState<string | null>(null);
-  const [pendingMessage, setPendingMessage] = useState<string | null>(null);
+  const [pendingMessage, setPendingMessage] = useState<{ content: string; images?: Array<{ type: 'image'; data: string; mimeType: string }> } | null>(null);
   const [showScrollBtn, setShowScrollBtn] = useState(false);
   const creatingRef = useRef(false);
   const scrollRef = useRef<HTMLDivElement>(null);
@@ -72,7 +72,7 @@ export function ChatView() {
   useEffect(() => {
     if (conversationId && connected && pendingMessage) {
       const timer = setTimeout(() => {
-        send(pendingMessage);
+        send(pendingMessage.content, pendingMessage.images);
         setPendingMessage(null);
       }, 300);
       return () => clearTimeout(timer);
@@ -108,10 +108,10 @@ export function ChatView() {
   }, [removeMessage]);
 
   // Delayed conversation creation
-  const handleSendNew = useCallback(async (content: string) => {
+  const handleSendNew = useCallback(async (content: string, images?: Array<{ data: string; mimeType: string }>) => {
     if (creatingRef.current) return;
     creatingRef.current = true;
-    setPendingMessage(content);
+    setPendingMessage({ content, images });
 
     try {
       const newId = await createConversation(content.slice(0, 30), selectedAccountId || undefined);
@@ -131,7 +131,7 @@ export function ChatView() {
     if (conversationId) {
       send(content, images);
     } else {
-      handleSendNew(content);
+      handleSendNew(content, images);
     }
   }, [send, quote, conversationId]);