fix(h5-chat): resolve logged-in blank page from canSubmit TDZ

Move canSubmit above sendButtonLabel so authenticated ChatPanel render no longer throws before initialization.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/components/ChatPanel.tsx

@@ -521,6 +521,7 @@ export function ChatPanel({
       : chatState === 'waiting'
         ? '请求已提交…'
         : null;
+  const canSubmit = input.trim() || pendingImages.length > 0 || pendingFiles.length > 0;
   const sendButtonLabel =
     uploadingImage || uploadingFile
       ? '上传中…'
@@ -579,7 +580,6 @@ export function ChatPanel({
   };
 
   const voiceDisabled = inputBlocked || uploadingImage || uploadingFile;
-  const canSubmit = input.trim() || pendingImages.length > 0 || pendingFiles.length > 0;
   const uploadDisabled = !canUpload || busy || uploadingImage || uploadingFile || offlineBlocked || !!pendingTool;
 
   const revokePendingImage = (item: PendingChatImage) => {