feat: 智能体精选排序与新对话智能体选择器

- 后端新增 featured_order 字段及精选排序 API（/agents/selector、/agents/{id}/featured、/agents/featured/order），移除 user_agent_pin 表
- 前端新对话页 (ChatPage) 与输入框 (InputBox) 接入 agent-selector，选中后跳转 AgentChatPage 并通过 sessionStorage 透传首条消息
- 新增管理员智能体管理弹窗 (agent-manage-dialog) 支持精选添加/移除/上下移动

frontend-web/src/pages/AgentChatPage.tsx

@@ -3,11 +3,10 @@
 import { BotIcon, PlusSquare } from "lucide-react";
 import { useParams, useRouter } from "next/navigation";
 import { useRouteBase } from "@/core/route-base";
-import { useCallback, useEffect, useState } from "react";
+import { useCallback, useEffect, useRef, useState } from "react";
 
 import type { PromptInputMessage } from "@/components/ai-elements/prompt-input";
 import { Button } from "@/components/ui/button";
-import { AgentWelcome } from "@/components/workspace/agent-welcome";
 import { ArtifactTrigger } from "@/components/workspace/artifacts";
 import { ChatBox, useThreadChat } from "@/components/workspace/chats";
 import { ExportTrigger } from "@/components/workspace/export-trigger";
@@ -56,6 +55,11 @@ export default function AgentChatPage() {
     }
   }, [isNewThread, threadId]);
 
+  // Auto-submit a message that the user typed on ChatPage right before
+  // selecting this agent. ChatPage stashed it in sessionStorage so we don't
+  // depend on router state (the next/navigation shim doesn't carry it).
+  const autoSubmitDoneRef = useRef(false);
+
   const { showNotification } = useNotification();
   const [thread, sendMessage] = useThreadStream({
     threadId: isNewThread ? undefined : threadId,
@@ -100,6 +104,29 @@ export default function AgentChatPage() {
     [sendMessage, threadId, agent_id],
   );
 
+  useEffect(() => {
+    if (autoSubmitDoneRef.current) return;
+    if (!isNewThread || hasStartedConversation) return;
+    let raw: string | null = null;
+    try {
+      raw = sessionStorage.getItem("pendingAgentMessage");
+    } catch {
+      return;
+    }
+    if (!raw) return;
+    try {
+      const parsed = JSON.parse(raw) as { agentId?: string; text?: string };
+      if (parsed.agentId !== agent_id || !parsed.text) {
+        return;
+      }
+      autoSubmitDoneRef.current = true;
+      sessionStorage.removeItem("pendingAgentMessage");
+      handleSubmit({ text: parsed.text, files: [] });
+    } catch {
+      sessionStorage.removeItem("pendingAgentMessage");
+    }
+  }, [agent_id, hasStartedConversation, handleSubmit, isNewThread]);
+
   const handleClarificationSubmit = useCallback(
     (answer: string) => {
       setHasStartedConversation(true);
@@ -116,7 +143,12 @@ export default function AgentChatPage() {
     ? MESSAGE_LIST_DEFAULT_PADDING_BOTTOM +
       MESSAGE_LIST_FOLLOWUPS_EXTRA_PADDING_BOTTOM
     : undefined;
-  const isLandingState = isNewThread && !hasStartedConversation;
+  // AgentChatPage skips the centered welcome/landing state entirely — when the
+  // user reaches this page they've already committed to an agent (either by
+  // selecting one on the homepage or by visiting the agent's URL), so we drop
+  // them straight into the conversation layout: messages area on top, input at
+  // the bottom. The agent badge in the header still identifies the agent.
+  const isLandingState = false;
 
   return (
     <ThreadContext.Provider value={{ thread }}>
@@ -198,9 +230,9 @@ export default function AgentChatPage() {
 
                 <InputBox
                   className={cn("bg-background/5 w-full -translate-y-4")}
-                  isNewThread={isLandingState}
+                  isNewThread={isNewThread}
                   threadId={threadId}
-                  autoFocus={isLandingState}
+                  autoFocus={isNewThread}
                   status={
                     thread.error
                       ? "error"
@@ -209,11 +241,6 @@ export default function AgentChatPage() {
                         : "ready"
                   }
                   context={settings.context}
-                  extraHeader={
-                    isLandingState && (
-                      <AgentWelcome agent={agent} agentName={agent?.name ?? agent_id} />
-                    )
-                  }
                   disabled={env.NEXT_PUBLIC_STATIC_WEBSITE_ONLY === "true"}
                   onContextChange={(context) => setSettings("context", context)}
                   onFollowupsVisibilityChange={setShowFollowups}

frontend-web/src/pages/ChatPage.tsx

@@ -1,5 +1,6 @@
 "use client";
 
+import { useRouter } from "next/navigation";
 import { useCallback, useEffect, useMemo, useState } from "react";
 
 import { type PromptInputMessage } from "@/components/ai-elements/prompt-input";
@@ -34,6 +35,7 @@ import { cn } from "@/lib/utils";
 
 export default function ChatPage() {
   const routeBase = useRouteBase();
+  const router = useRouter();
   const { t } = useI18n();
   const [showFollowups, setShowFollowups] = useState(false);
   const [hasStartedConversation, setHasStartedConversation] = useState(false);
@@ -44,6 +46,7 @@ export default function ChatPage() {
   const { tokenUsageEnabled } = useModels();
   const { data: promptPrefixSettings } = usePromptPrefixSettings();
   const [promptPrefixOn, setPromptPrefixOn] = useState(false);
+  const [selectedAgentId, setSelectedAgentId] = useState<string | null>(null);
   const { selectedArtifact } = useArtifacts();
   useSpecificChatMode();
 
@@ -55,6 +58,7 @@ export default function ChatPage() {
     if (isNewThread) {
       setHasStartedConversation(false);
       setPromptPrefixOn(false);
+      setSelectedAgentId(null);
     }
   }, [isNewThread, threadId]);
 
@@ -105,6 +109,32 @@ export default function ChatPage() {
 
   const handleSubmit = useCallback(
     (message: PromptInputMessage) => {
+      // If the user picked an agent before sending the opening turn, hand off
+      // to AgentChatPage so the conversation runs against that agent. We stash
+      // the pending text in sessionStorage because the next/navigation shim
+      // doesn't carry router state across hash-route pushes. File attachments
+      // are bound to the current thread upload directory and would not match
+      // the new thread, so we skip the handoff when files are present and let
+      // the message run on Lead Agent instead.
+      if (
+        selectedAgentId &&
+        isNewThread &&
+        !hasStartedConversation &&
+        message.text &&
+        (!message.files || message.files.length === 0)
+      ) {
+        try {
+          sessionStorage.setItem(
+            "pendingAgentMessage",
+            JSON.stringify({ agentId: selectedAgentId, text: message.text }),
+          );
+        } catch {
+          // sessionStorage may be unavailable in private mode; fall through.
+        }
+        router.push(`/page/workspace/agents/${selectedAgentId}/chats/new`);
+        return;
+      }
+
       // Only the opening turn of a brand-new thread may carry the prefix.
       const shouldApplyPrefix =
         isNewThread &&
@@ -140,6 +170,8 @@ export default function ChatPage() {
       hasStartedConversation,
       promptPrefixOn,
       promptPrefixSettings,
+      selectedAgentId,
+      router,
       settings.context.writing_mode,
       writingArtifactPath,
     ],
@@ -258,6 +290,14 @@ export default function ChatPage() {
                         setSettings("context", context)
                       }
                       promptPrefix={promptPrefixProp}
+                      agentSelector={
+                        isLandingState
+                          ? {
+                              selectedAgentId,
+                              onAgentChange: setSelectedAgentId,
+                            }
+                          : undefined
+                      }
                       onFollowupsVisibilityChange={setShowFollowups}
                       onSubmit={handleSubmit}
                       onStop={handleStop}