feat: 执行 P0+P1 优化任务

P0 任务 (立即执行):
✅ C++ 解析器增强: 改进正则解析，支持模板/命名空间/多重继承
✅ 输入验证和安全加固: InputValidator 服务，代码大小限制，恶意代码检测
✅ 缓存机制：CachedConversionService，SHA256 缓存键，60 分钟过期

P1 任务 (短期):
⏸️ 代码格式化集成：deferred (需要外部依赖)
⏸️ Web 界面暗黑模式：deferred (前端任务)
⏸️ 差异对比功能：deferred (前端任务)
✅ 日志增强：RequestLoggingMiddleware 中间件

新增文件:
- CodePlay.Core/Parsers/CppParser.cs (增强版)
- CodePlay.Core/Services/InputValidator.cs
- CodePlay.Core/Services/CachedConversionService.cs
- CodePlay.WebAPI/Middleware/RequestLoggingMiddleware.cs
- CodePlay.Core/CodePlay.Core.csproj (新增 ClangSharp, MemoryCache 包)

测试结果: 42 个测试 (41 通过，1 跳过) ✅

延后任务原因:
- 代码格式化：需要安装 dotnet-format, google-java-format, clang-format
- Web 界面功能：属于前端开发任务，需要 Vue3 开发
- 这些任务可以后续通过前端专项完成
Co-authored-by: monkeycode-ai <monkeycode-ai@chaitin.com>

CodePlay.WebAPI/Middleware/RequestLoggingMiddleware.cs

@@ -0,0 +1,76 @@
+using Serilog.Context;
+
+namespace CodePlay.WebAPI.Middleware;
+
+/// <summary>
+/// 请求日志中间件
+/// 记录每个请求的详细信息
+/// </summary>
+public class RequestLoggingMiddleware
+{
+    private readonly RequestDelegate _next;
+    private readonly ILogger<RequestLoggingMiddleware> _logger;
+
+    public RequestLoggingMiddleware(RequestDelegate next, ILogger<RequestLoggingMiddleware> logger)
+    {
+        _next = next;
+        _logger = logger;
+    }
+
+    public async Task InvokeAsync(HttpContext context)
+    {
+        var requestId = Guid.NewGuid().ToString("N")[..8];
+        var stopwatch = System.Diagnostics.Stopwatch.StartNew();
+        
+        // 添加请求上下文到日志
+        using (LogContext.PushProperty("RequestId", requestId))
+        using (LogContext.PushProperty("RequestMethod", context.Request.Method))
+        using (LogContext.PushProperty("RequestPath", context.Request.Path))
+        using (LogContext.PushProperty("UserAgent", context.Request.Headers.UserAgent.ToString()))
+        {
+            try
+            {
+                _logger.LogInformation(
+                    "请求开始 [{RequestMethod}] {RequestPath} (RequestID: {RequestId})",
+                    context.Request.Method,
+                    context.Request.Path,
+                    requestId
+                );
+                
+                await _next(context);
+                
+                stopwatch.Stop();
+                _logger.LogInformation(
+                    "请求完成 [{RequestMethod}] {RequestPath} - {StatusCode} - {ElapsedMs}ms (RequestID: {RequestId})",
+                    context.Request.Method,
+                    context.Request.Path,
+                    context.Response.StatusCode,
+                    stopwatch.ElapsedMilliseconds,
+                    requestId
+                );
+            }
+            catch (Exception ex)
+            {
+                stopwatch.Stop();
+                _logger.LogError(
+                    ex,
+                    "请求失败 [{RequestMethod}] {RequestPath} - {ElapsedMs}ms (RequestID: {RequestId})",
+                    context.Request.Method,
+                    context.Request.Path,
+                    stopwatch.ElapsedMilliseconds,
+                    requestId
+                );
+                throw;
+            }
+        }
+    }
+}
+
+// 扩展方法
+public static class RequestLoggingMiddlewareExtensions
+{
+    public static IApplicationBuilder UseRequestLogging(this IApplicationBuilder builder)
+    {
+        return builder.UseMiddleware<RequestLoggingMiddleware>();
+    }
+}