fix: show and dismiss teacher introductions as one group

tests/e2e/fixtures/teacher-preview-layout.tsx

@@ -19,7 +19,7 @@ export function Layout() {
   const [refreshStatus, setRefreshStatus] = useState<'idle' | 'success' | 'error'>('idle');
   const [selected, setSelected] = useState(0);
   const welcomeMode = new URLSearchParams(location.search).has('welcomes');
-  const [dismissed, setDismissed] = useState<string[]>([]);
+  const [dismissed, setDismissed] = useState(false);
   const agents = Array.from({ length: count }, (_, index) => ({
     teacher_id: `agent-${index}`, version: index + 1, is_default: index === 0,
     definition: { config_id: `agent-${index}`, name: `智能体${index + 1}`, avatar_id: 'avatar-06',
@@ -31,8 +31,8 @@ export function Layout() {
     definition: agents[selected]?.definition ?? { name: '编程老师', avatar_id: 'avatar-06' },
     invitation: !welcomeMode && visible ? { response: long ? '你刚才说想做一个宠物游戏。我们一起想想，什么样的小动作，会让你愿意一直陪它玩下去？可以先挑一个最想试的想法。' : '有什么编程问题想一起讨论？' } : null,
     welcome: null, enabled: true, loading: false, checking: false, error: null,
-    welcomes: welcomeMode && !open ? agents.flatMap((agent, index) => dismissed.includes(agent.teacher_id) ? [] : [{ agentId: agent.teacher_id, definition: agent.definition, text: agent.definition.description, tone: index % 3 }]) : [],
-    dismissWelcome: (id: string) => setDismissed(ids => [...new Set([...ids, id])]),
+    welcomes: welcomeMode && !open && !dismissed ? agents.map((agent, index) => ({ agentId: agent.teacher_id, definition: agent.definition, text: agent.definition.description, tone: index % 3 })) : [],
+    dismissWelcomes: () => setDismissed(true),
     refreshing, refreshStatus,
     refresh: async () => {
       setRefreshing(true);