ui: add hint that session tests don't send messages to platform chats

- Add sessions.testHint i18n text (zh-CN + en)
- Show hint next to 'Test All' button on sessions page

app/sessions/page.tsx

@@ -257,6 +257,7 @@ function SessionList({ agentId }: { agentId: string }) {
           >
             {testingAll ? t("sessions.testingAll") : t("sessions.testAll")}
           </button>
+          <span className="text-xs text-[var(--text-muted)]">{t("sessions.testHint")}</span>
           <Link
             href="/sessions"
             className="px-4 py-2 rounded-lg bg-[var(--card)] border border-[var(--border)] text-sm hover:border-[var(--accent)] transition"

lib/i18n.tsx

@@ -148,6 +148,7 @@ const translations: Record<Locale, Record<string, string>> = {
     "sessions.selectAgent": "选择一个机器人查看其会话列表",
     "sessions.testAll": "🧪 测试全部",
     "sessions.testingAll": "⏳ 测试中...",
+    "sessions.testHint": "测试验证 Agent 是否能响应，消息不会出现在飞书/Discord 会话中",
     "sessions.testAllResult": "测试完成",
     "sessions.testAllOk": "通过",
     "sessions.testAllFail": "失败",
@@ -310,6 +311,7 @@ const translations: Record<Locale, Record<string, string>> = {
     "sessions.selectAgent": "Select an agent to view its sessions",
     "sessions.testAll": "🧪 Test All",
     "sessions.testingAll": "⏳ Testing...",
+    "sessions.testHint": "Tests verify agent responsiveness only. Messages won't appear in Feishu/Discord chats.",
     "sessions.testAllResult": "Test complete",
     "sessions.testAllOk": "passed",
     "sessions.testAllFail": "failed",