fix: Gemini 图片生成流程添加智能对话回复

- 在 Gemini/Huanke-Gemini 图片生成流程中添加 conversationalReply 发送逻辑
- 与 Alibaba 图片生成流程保持一致
- 确保无限画布中的智能自动模式能显示 AI 对话回复

app/(chat)/api/chat/route.ts

@@ -752,6 +752,46 @@ export async function POST(request: Request) {
       
       const geminiStream = createUIMessageStream({
         execute: async ({ writer }) => {
+          // 🆕 如果是智能模式且有对话回复，先发送对话消息让用户看到
+          // 在消息末尾加上特殊标记，告诉前端"图片正在生成中"
+          const messageWithMarker = smartAutoFriendlyMessage 
+            ? `${smartAutoFriendlyMessage}\n\n<!-- GENERATING_IMAGE -->`
+            : null;
+          
+          if (messageWithMarker) {
+            const chatMessageId = generateUUID();
+            console.log("[Chat API] 💬 Gemini: Sending conversational reply first:", smartAutoFriendlyMessage);
+            
+            // 发送带标记的对话消息
+            writer.write({
+              type: "data-appendMessage",
+              data: JSON.stringify({
+                id: chatMessageId,
+                role: "assistant",
+                parts: [{ type: "text", text: messageWithMarker }],
+              }),
+            });
+            
+            // 保存对话消息到数据库（不带标记，纯对话）
+            await saveMessages({
+              messages: [
+                {
+                  id: chatMessageId,
+                  chatId: id,
+                  role: "assistant",
+                  parts: [{ type: "text", text: smartAutoFriendlyMessage }],
+                  attachments: [],
+                  createdAt: new Date(),
+                  videoStorageStatus: null,
+                  temporaryVideoUrl: null,
+                  permanentVideoUrl: null,
+                  archivedAt: null,
+                  videoMetadata: null,
+                },
+              ],
+            });
+          }
+          
           // 🆕 尝试生成图片的函数（支持备用模型切换）
           const tryGenerateImage = async (modelIdToUse: string, isRetry = false): Promise<string> => {
             console.log(`[Chat API] ${isRetry ? "🔄 Retry with fallback" : "🚀 Trying"} model: ${modelIdToUse}`);