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/routes/chat.test.ts

@@ -12,18 +12,24 @@ import { createMigratedMemoryTestDatabase } from "../../helpers";
 const MODE: RuntimeMode = "test";
 
 void mock.module("ai", () => ({
+  createAgentUIStreamResponse: () =>
+    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: "mock", usage: {} }),
+  generateText: () => Promise.resolve({ text: "", usage: {} }),
   stepCountIs: () => () => true,
-  streamText: () => ({
-    text: Promise.resolve("test reply from AI"),
-    toUIMessageStreamResponse: () =>
-      new Response('data: {"type":"text","text":"test reply from AI"}\n\n', {
-        headers: { "Content-Type": "text/event-stream" },
-      }),
-  }),
+  tool: () => ({ execute: async () => await Promise.resolve({}) }),
+  ToolLoopAgent: function M() {
+    // no-op: createAgentUIStreamResponse handles streaming
+  },
 }));
 
 async function createConversationViaHandler(req: Request, db: Database): Promise<Response> {