refactor: 标题生成重构、UI样式优化、测试增强

- 将标题生成逻辑提取为独立函数，提前到Agent调用前非阻塞执行

- 修复模型/供应商不存在时的HTTP状态码 500→400

- ChatPanel: 分离模型选择useEffect、CSS类替代内联样式、按钮样式统一

- use-conversations: fetchConversations/fetchMessages改用handleResponse去重

- 聊天面板滚动优化(scroll-behavior: smooth, overflow-anchor: auto)

- 测试: mock支持onFinish回调，新增首次消息标题生成测试

- 移除未使用的SendMessageRequest接口

tests/server/routes/chat.test.ts

@@ -13,19 +13,33 @@ import { createMigratedMemoryTestDatabase } from "../../helpers";
 const MODE: RuntimeMode = "test";
 
 void mock.module("ai", () => ({
-  createAgentUIStreamResponse: () =>
-    Promise.resolve(
+  createAgentUIStreamResponse: (opts: {
+    agent: unknown;
+    messages: unknown[];
+    onFinish:
+      | ((event: { finishReason?: string; responseMessage: { parts?: Array<{ text: string; type: string }> } }) => void)
+      | undefined;
+  }) => {
+    if (opts.onFinish) {
+      opts.onFinish({
+        responseMessage: {
+          parts: [{ text: "test reply from AI", type: "text" }],
+        },
+      });
+    }
+    return Promise.resolve(
       new Response(
         'data: {"type":"start-step"}\n\ndata: {"type":"text-start","id":"txt-1"}\n\ndata: {"type":"text-delta","id":"txt-1","delta":"test reply from AI"}\n\ndata: {"type":"text-end","id":"txt-1"}\n\ndata: {"type":"finish-step"}\n\ndata: {"type":"finish"}\n\n',
         {
           headers: { "Content-Type": "text/event-stream" },
         },
       ),
-    ),
+    );
+  },
   createProviderRegistry: () => ({
     languageModel: () => ({}),
   }),
-  generateText: () => Promise.resolve({ text: "", usage: {} }),
+  generateText: () => Promise.resolve({ text: "AI总结标题", usage: {} }),
   stepCountIs: () => () => true,
   tool: () => ({ execute: async () => await Promise.resolve({}) }),
   ToolLoopAgent: function M() {
@@ -593,8 +607,56 @@ describe("聊天 API 路由", () => {
           db,
         );
         const msgBody = (await msgRes.json()) as { items: Message[] };
-        expect(msgBody.items.length).toBeGreaterThanOrEqual(1);
+        expect(msgBody.items.length).toBeGreaterThanOrEqual(2);
         expect(msgBody.items.some((m) => m.role === "user")).toBe(true);
+        expect(msgBody.items.some((m) => m.role === "assistant")).toBe(true);
+        handle.close();
+      } finally {
+        handle.cleanup();
+      }
+    });
+
+    test("首次发送消息时触发标题生成", async () => {
+      const handle = createMigratedMemoryTestDatabase("chat-send-title");
+      try {
+        const db = handle.db;
+        const projectId = seedProject(db);
+        const providerId = seedProvider(db);
+        const modelId = seedModel(db, providerId);
+
+        const createRes = await createConversationViaHandler(
+          new Request(`http://localhost/api/projects/${projectId}/conversations`, {
+            body: JSON.stringify({}),
+            headers: { "Content-Type": "application/json" },
+            method: "POST",
+          }),
+          db,
+        );
+        const created = ((await createRes.json()) as { conversation: Conversation }).conversation;
+        expect(created.title).toBe("新会话");
+
+        await sendChatViaHandler(
+          new Request(`http://localhost/api/projects/${projectId}/chat`, {
+            body: JSON.stringify({
+              conversationId: created.id,
+              messages: [{ parts: [{ text: "请帮我分析一下这个项目的性能瓶颈", type: "text" }], role: "user" }],
+              modelDbId: modelId,
+            }),
+            headers: { "Content-Type": "application/json" },
+            method: "POST",
+          }),
+          db,
+        );
+
+        await new Promise((resolve) => setTimeout(resolve, 50));
+
+        const getRes = await getConversationViaHandler(
+          new Request(`http://localhost/api/projects/${projectId}/conversations/${created.id}`),
+          db,
+        );
+        const body = (await getRes.json()) as { conversation: Conversation };
+        expect(body.conversation.title).not.toBe("新会话");
+        expect(body.conversation.title).toBe("AI总结标题");
         handle.close();
       } finally {
         handle.cleanup();