feat(agents): 智能体常用问题——侧边栏展示并一键提问

新增 common_questions(常用问题)字段：后端贯通 agents_config、
config.yaml 读写与 create/update API，前端 Agent 类型补充字段并在
AgentChatPage 新增 AgentInfoSidebar 组件展示常用问题，点击即填充并提交。

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

frontend-web/src/pages/AgentChatPage.tsx

@@ -7,6 +7,7 @@ import { useCallback, useEffect, useRef, useState } from "react";
 
 import type { PromptInputMessage } from "@/components/ai-elements/prompt-input";
 import { Button } from "@/components/ui/button";
+import { AgentInfoSidebar } from "@/components/workspace/agent-info-sidebar";
 import { AgentWelcome } from "@/components/workspace/agent-welcome";
 import { ArtifactTrigger } from "@/components/workspace/artifacts";
 import { ChatBox, useThreadChat } from "@/components/workspace/chats";
@@ -285,6 +286,16 @@ export default function AgentChatPage() {
               </div>
             </div>
           </main>
+
+          <AgentInfoSidebar
+            agent={agent}
+            agentName={agentDisplayName}
+            disabled={
+              thread.isLoading ||
+              env.NEXT_PUBLIC_STATIC_WEBSITE_ONLY === "true"
+            }
+            onAskQuestion={(text) => handleSubmit({ text, files: [] })}
+          />
         </div>
       </ChatBox>
     </ThreadContext.Provider>