feat(dc): Complete Tool C Day 5 - AI Chat + Ant Design X Integration

Summary:
- Upgrade to Ant Design 6.0.1 + install Ant Design X (2.1.0) + X SDK (2.1.0)
- Develop frontend common capability layer: Chat component library (~968 lines)
  * ChatContainer.tsx - Core container component
  * MessageRenderer.tsx - Message renderer
  * CodeBlockRenderer.tsx - Code block renderer with syntax highlighting
  * Complete TypeScript types and documentation
- Integrate ChatContainer into Tool C
- Fix 7 critical UI issues:
  * AG Grid module registration error
  * UI refinement (borders, shadows, gradients)
  * Add AI welcome message
  * Auto-clear input field after sending
  * Remove page scrollbars
  * Manual code execution (not auto-run)
  * Support simple Q&A (new /ai/chat API)
- Complete end-to-end testing
- Update all documentation (4 status docs + 6 dev logs)

Technical Stack:
- Frontend: React 19 + Ant Design 6.0 + Ant Design X 2.1
- Components: Bubble, Sender from @ant-design/x
- Total code: ~5418 lines

Status: Tool C MVP completed, production ready

frontend-v2/src/main.tsx

@@ -1,10 +1,24 @@
 import React from 'react'
 import ReactDOM from 'react-dom/client'
+import { ConfigProvider } from 'antd'
+import zhCN from 'antd/locale/zh_CN'
 import App from './App.tsx'
 import './index.css'
 
 ReactDOM.createRoot(document.getElementById('root')!).render(
   <React.StrictMode>
-    <App />
+    <ConfigProvider
+      locale={zhCN}
+      theme={{
+        cssVar: true,  // ⭐ 启用 CSS 变量（Ant Design 6.0 新特性）
+        token: {
+          colorPrimary: '#10b981', // emerald-500（工具C主题色）
+          borderRadius: 8,
+          fontSize: 14,
+        },
+      }}
+    >
+      <App />
+    </ConfigProvider>
   </React.StrictMode>,
 )