Add conceptual docs on accessing HttpContext (#771)

* Add doc with sample on accessing HttpContext
* Apply suggestions from PR review

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

docs/concepts/httpcontext/samples/Program.cs

@@ -0,0 +1,26 @@
+using HttpContext.Tools;
+
+var builder = WebApplication.CreateBuilder(args);
+
+// Add services to the container.
+
+builder.Services.AddMcpServer()
+    .WithHttpTransport()
+    .WithTools<ContextTools>();
+
+// <snippet_AddHttpContextAccessor>
+builder.Services.AddHttpContextAccessor();
+// </snippet_AddHttpContextAccessor>
+
+builder.Logging.AddConsole(options =>
+{
+    options.LogToStandardErrorThreshold = LogLevel.Information;
+});
+
+var app = builder.Build();
+
+app.UseHttpsRedirection();
+
+app.MapMcp();
+
+app.Run();