feat: add save feedback prompts, featured agent fields, dynamic Dify API config, and chat improvements

- Add success/error feedback messages near submit buttons in all admin forms
- Display success prompt for 1s before redirect after save
- Show API error details on save failure
- Add isFeatured/featuredOrder fields to Agent model and admin UI
- Add difyApiUrl/difyApiKey fields for per-agent Dify API configuration
- Show featured badge column in agent admin list
- Display featured agents on homepage sorted by order
- Refactor chat page streaming with AbortController and stable userId
- Improve Dify API proxy to use per-agent credentials

app/agents/[slug]/chat/page.tsx

@@ -48,8 +48,10 @@ export default function AgentChatPage() {
   const [currentConversationId, setCurrentConversationId] = useState<number | null>(null)
   const [upstreamConversationId, setUpstreamConversationId] = useState<string>('')
   const [loadingConversations, setLoadingConversations] = useState(false)
+  const [abortController, setAbortController] = useState<AbortController | null>(null)
 
   const messagesEndRef = useRef<HTMLDivElement>(null)
+  const userIdRef = useRef<string>('user-' + Math.random().toString(36).slice(2, 10))
 
   const CHAT_API_URL = '/api/chat'
 
@@ -190,8 +192,6 @@ export default function AgentChatPage() {
       })
 
       const assistantMessageId = (Date.now() + 1).toString()
-      let assistantContent = ''
-      let upstreamConvId = upstreamConversationId
 
       setMessages(prev => [...prev, {
         id: assistantMessageId,
@@ -200,70 +200,70 @@ export default function AgentChatPage() {
         timestamp: new Date(),
       }])
 
+      const controller = new AbortController()
+      setAbortController(controller)
+
       const response = await fetch(CHAT_API_URL, {
         method: 'POST',
         headers: { 'Content-Type': 'application/json' },
         body: JSON.stringify({
+          agentId: agent.id,
           inputs: {},
           query: currentInput,
           response_mode: 'streaming',
           conversation_id: upstreamConversationId,
-          user: 'user-' + Date.now(),
+          user: userIdRef.current,
         }),
+        signal: controller.signal,
       })
 
-      const reader = response.body?.getReader()
-      const decoder = new TextDecoder()
+      if (!response.ok) {
+        throw new Error('Chat request failed')
+      }
 
-      if (reader) {
-        let buffer = ''
-        while (true) {
-          const { done, value } = await reader.read()
-          if (done) break
-          buffer += decoder.decode(value, { stream: true })
-          const lines = buffer.split('\n')
-          buffer = lines.pop() || ''
-          for (const line of lines) {
-            if (line.startsWith('data: ')) {
-              try {
-                const json = JSON.parse(line.slice(6))
-                if (json.conversation_id) {
-                  upstreamConvId = json.conversation_id
-                }
-                const token = json.answer || json.message || ''
-                if (token) {
-                  assistantContent += token
-                  setMessages(prev => prev.map(msg =>
-                    msg.id === assistantMessageId
-                      ? { ...msg, content: assistantContent }
-                      : msg
-                  ))
-                }
-              } catch (e) {
-                // ignore parse errors
+      const reader = response.body!.getReader()
+      const decoder = new TextDecoder()
+      let buffer = ''
+      let accumulatedContent = ''
+      let finalConvId = upstreamConversationId
+
+      while (true) {
+        const { done, value } = await reader.read()
+        if (done) break
+
+        buffer += decoder.decode(value, { stream: true })
+        const lines = buffer.split('\n')
+        buffer = lines.pop() || ''
+
+        for (const line of lines) {
+          if (line.startsWith('data: ')) {
+            try {
+              const data = JSON.parse(line.slice(6))
+              if (data.event === 'message' && data.answer) {
+                accumulatedContent += data.answer
+                setMessages(prev => prev.map(msg =>
+                  msg.id === assistantMessageId
+                    ? { ...msg, content: accumulatedContent }
+                    : msg
+                ))
+              } else if (data.event === 'message_end') {
+                finalConvId = data.conversation_id || finalConvId
               }
+            } catch (e) {
+              // skip invalid JSON
             }
           }
         }
       }
 
-      setUpstreamConversationId(upstreamConvId)
-
-      if (!assistantContent) {
-        setMessages(prev => prev.map(msg =>
-          msg.id === assistantMessageId
-            ? { ...msg, content: '抱歉，我暂时无法回答这个问题。' }
-            : msg
-        ))
-        assistantContent = '抱歉，我暂时无法回答这个问题。'
-      }
+      setUpstreamConversationId(finalConvId)
 
       await fetch(`/api/conversations/${conversationId}/messages`, {
         method: 'POST',
         headers: { 'Content-Type': 'application/json' },
         body: JSON.stringify({
           role: 'assistant',
-          content: assistantContent,
+          content: accumulatedContent,
         }),
       })
     } catch (error) {