Add file-based MCP server sample for .NET 10 (#3) (#931)

samples/FileBasedMcpServer/Program.cs

@@ -0,0 +1,30 @@
+#!/usr/bin/env -S dotnet run --
+#:package Microsoft.Extensions.Hosting
+#:project ../../src/ModelContextProtocol/ModelContextProtocol.csproj
+
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Hosting;
+using Microsoft.Extensions.Logging;
+using ModelContextProtocol.Server;
+using System.ComponentModel;
+
+var builder = Host.CreateApplicationBuilder(args);
+
+builder.Services.AddMcpServer()
+    .WithStdioServerTransport()
+    .WithTools<EchoTool>();
+
+builder.Logging.AddConsole(options =>
+{
+    options.LogToStandardErrorThreshold = LogLevel.Trace;
+});
+
+await builder.Build().RunAsync();
+
+// File-scoped tool class
+[McpServerToolType]
+file class EchoTool
+{
+    [McpServerTool(Name = "echo"), Description("Echoes the message back to the client.")]
+    public static string Echo([Description("The message to echo back.")] string message) => $"Echo: {message}";
+}