feat: 实现 Blazor 前端界面 (Task 4.3) 和 CLI 工具 (Task 5.1)

Task 4.3 - Blazor 前端界面:
- 创建 CodePlay.WebUI Blazor Server 项目
- 实现 Converter.razor 代码转换页面
- 提供代码输入、语言选择、转换按钮
- 显示转换结果、TODO 列表和问题列表
- 更新导航菜单
- 注册 ConversionService 服务

Task 5.1 - CLI 命令行工具:
- 集成 System.CommandLine 库
- 实现 convert 命令（代码转换）
- 实现 list 命令（列出支持的转换）
- 实现 check 命令（检查是否支持）
- 支持 -s/-t 指定源/目标语言
- 支持 -i/-o 指定输入/输出文件
- 支持 -v 指定验证轮次
- 支持 -c 指定配置文件

测试:
- CLI help 命令: ✅
- CLI list 命令: ✅
- CLI convert 命令: ✅ (成功转换 C# 到 Java)
Co-authored-by: monkeycode-ai <monkeycode-ai@chaitin.com>

CodePlay.WebUI/wwwroot/app.css

@@ -0,0 +1,51 @@
+html, body {
+    font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
+}
+
+a, .btn-link {
+    color: #006bb7;
+}
+
+.btn-primary {
+    color: #fff;
+    background-color: #1b6ec2;
+    border-color: #1861ac;
+}
+
+.btn:focus, .btn:active:focus, .btn-link.nav-link:focus, .form-control:focus, .form-check-input:focus {
+  box-shadow: 0 0 0 0.1rem white, 0 0 0 0.25rem #258cfb;
+}
+
+.content {
+    padding-top: 1.1rem;
+}
+
+h1:focus {
+    outline: none;
+}
+
+.valid.modified:not([type=checkbox]) {
+    outline: 1px solid #26b050;
+}
+
+.invalid {
+    outline: 1px solid #e50000;
+}
+
+.validation-message {
+    color: #e50000;
+}
+
+.blazor-error-boundary {
+    background: url(data:image/svg+xml;base64,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) no-repeat 1rem/1.8rem, #b32121;
+    padding: 1rem 1rem 1rem 3.7rem;
+    color: white;
+}
+
+    .blazor-error-boundary::after {
+        content: "An error has occurred."
+    }
+
+.darker-border-checkbox.form-check-input {
+    border-color: #929292;
+}