refactor: 聊天室 Agent 重构 — ToolLoopAgent + 论坛式布局

后端:
- 删除 agent-stream.ts，新建 alfred-agent.ts (ToolLoopAgent 工厂)
- 新建 get-current-time.ts 工具 (zod schema)
- 重构 send.ts: createAgentUIStreamResponse + onFinish 可靠持久化

前端:
- 删除 MessageBubble.tsx，新建 ToolCallCard.tsx (四态)
- 重构 ChatPanel.tsx: 论坛式 Card 布局 + PartRenderer 分派
- 移除 @ant-design/x 依赖，改用 antd 组件 + streamdown

依赖:
+ zod + streamdown
- @ant-design/x - @ant-design/x-markdown

测试: 306 pass, typecheck/lint 0 errors

tests/server/ai/tools/get-current-time.test.ts

@@ -0,0 +1,25 @@
+import { describe, expect, test } from "bun:test";
+
+import { formatCurrentTime } from "../../../../src/server/ai/tools/get-current-time";
+
+describe("getCurrentTime 工具", () => {
+  test("formatCurrentTime 返回 ISO/local/timestamp", () => {
+    const result = formatCurrentTime();
+    expect(result).toBeDefined();
+    expect(typeof result.iso).toBe("string");
+    expect(typeof result.local).toBe("string");
+    expect(typeof result.timestamp).toBe("number");
+  });
+
+  test("formatCurrentTime 指定 timezone", () => {
+    const result = formatCurrentTime("Asia/Shanghai");
+    expect(result).toBeDefined();
+    expect(typeof result.local).toBe("string");
+  });
+
+  test("formatCurrentTime 无效 timezone 优雅降级", () => {
+    const result = formatCurrentTime("Invalid/Zone");
+    expect(result).toBeDefined();
+    expect(typeof result.local).toBe("string");
+  });
+});