feat(chat): 引入 @ant-design/x 组件 — Sender/Conversations/XMarkdown 替代手动拼装

- ConfigProvider → XProvider（ConsoleShell + test-utils）
- ChatSidebar → Conversations（menu dropdown + MoreOutlined trigger）
- ChatInputArea → Sender（footer 左右排版 + 模型 Select + 自动清空）
- Streamdown → XMarkdown（streaming hasNextChunk 映射 AI SDK 状态）
- CSS 清理 ~94 行废弃样式，新增统一布局规则
- 删除 streamdown 依赖

tests/web/components/ChatPanel.test.tsx

@@ -51,8 +51,8 @@ void mock.module("ai", () => ({
   },
 }));
 
-function getSendButton() {
-  return screen.getByRole("button", { name: /发.*送/ });
+function getSenderTextarea() {
+  return screen.getByPlaceholderText("输入消息...");
 }
 
 function setupFetchMock() {
@@ -90,8 +90,7 @@ describe("ChatPanel", () => {
 
       expect(screen.getByText("你好，我是阿福")).toBeTruthy();
       expect(screen.getByText("有什么我可以帮助你的吗？")).toBeTruthy();
-      expect(screen.getByPlaceholderText("输入消息...")).toBeTruthy();
-      expect(getSendButton()).toBeTruthy();
+      expect(getSenderTextarea()).toBeTruthy();
     });
   });
 
@@ -108,9 +107,9 @@ describe("ChatPanel", () => {
         }),
       );
 
-      const input = screen.getByPlaceholderText("输入消息...");
-      fireEvent.change(input, { target: { value: "你好" } });
-      fireEvent.click(getSendButton());
+      const textarea = getSenderTextarea();
+      fireEvent.change(textarea, { target: { value: "你好" } });
+      fireEvent.keyDown(textarea, { key: "Enter" });
 
       await waitFor(() => {
         expect(onCreated).toHaveBeenCalledWith("conv-new");
@@ -139,12 +138,12 @@ describe("ChatPanel", () => {
         }),
       );
 
-      const input = screen.getByPlaceholderText("输入消息...");
-      fireEvent.change(input, { target: { value: "测试输入" } });
-      fireEvent.click(getSendButton());
+      const textarea = getSenderTextarea();
+      fireEvent.change(textarea, { target: { value: "测试输入" } });
+      fireEvent.keyDown(textarea, { key: "Enter" });
 
       await waitFor(() => {
-        expect((input as HTMLTextAreaElement).value).toBe("测试输入");
+        expect((textarea as HTMLTextAreaElement).value).toBe("测试输入");
       });
     });
   });
@@ -161,7 +160,7 @@ describe("ChatPanel", () => {
       );
 
       expect(screen.queryByText("你好，我是阿福")).toBeNull();
-      expect(screen.getByPlaceholderText("输入消息...")).toBeTruthy();
+      expect(getSenderTextarea()).toBeTruthy();
     });
   });
 });