feat(agents): 智能体问答页落地态展示常用问题入口并默认展开简介栏

- 落地页 Hero 以"Hi，我是{名称}"问候，将管理员配置的常用问题渲染为可点击的引导气泡，点击即发起对话
- 右侧智能体简介栏改为默认展开，作为主要"专家信息"卡片，仍可手动收起

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend-web/src/pages/AgentChatPage.tsx

@@ -268,7 +268,16 @@ export default function AgentChatPage() {
                     context={settings.context}
                     extraHeader={
                       isLandingState && (
-                        <AgentWelcome agent={agent} agentName={agentDisplayName} />
+                        <AgentWelcome
+                          agent={agent}
+                          agentName={agentDisplayName}
+                          onAskQuestion={(text) =>
+                            handleSubmit({ text, files: [] })
+                          }
+                          disabled={
+                            env.NEXT_PUBLIC_STATIC_WEBSITE_ONLY === "true"
+                          }
+                        />
                       )
                     }
                     disabled={env.NEXT_PUBLIC_STATIC_WEBSITE_ONLY === "true"}