feat: add structured logging, Shouldly assertions, CPM, and project documentation

- Add Microsoft.Extensions.Logging + Serilog to NatsServer and NatsClient
- Convert all test assertions from xUnit Assert to Shouldly
- Add NSubstitute package for future mocking needs
- Introduce Central Package Management via Directory.Packages.props
- Add documentation_rules.md with style guide, generation/update rules, component map
- Generate 10 documentation files across 5 component folders (GettingStarted, Protocol, Subscriptions, Server, Configuration/Operations)
- Update CLAUDE.md with logging, testing, porting, agent model, CPM, and documentation guidance

tests/NATS.Server.Tests/IntegrationTests.cs

@@ -1,6 +1,7 @@
 using System.Net;
 using System.Net.Sockets;
 using System.Text;
+using Microsoft.Extensions.Logging.Abstractions;
 using NATS.Client.Core;
 using NATS.Server;
 
@@ -16,7 +17,7 @@ public class IntegrationTests : IAsyncDisposable
     public IntegrationTests()
     {
         _port = GetFreePort();
-        _server = new NatsServer(new NatsOptions { Port = _port });
+        _server = new NatsServer(new NatsOptions { Port = _port }, NullLoggerFactory.Instance);
         _serverTask = _server.StartAsync(_cts.Token);
         Thread.Sleep(200); // Let server start
     }
@@ -65,7 +66,7 @@ public class IntegrationTests : IAsyncDisposable
         await pub.PublishAsync("test.subject", "Hello NATS!");
 
         var result = await received.Task.WaitAsync(TimeSpan.FromSeconds(5));
-        Assert.Equal("Hello NATS!", result);
+        result.ShouldBe("Hello NATS!");
     }
 
     [Fact]
@@ -92,7 +93,7 @@ public class IntegrationTests : IAsyncDisposable
         await pub.PublishAsync("test.hello", "data");
 
         var result = await received.Task.WaitAsync(TimeSpan.FromSeconds(5));
-        Assert.Equal("test.hello", result);
+        result.ShouldBe("test.hello");
     }
 
     [Fact]
@@ -119,7 +120,7 @@ public class IntegrationTests : IAsyncDisposable
         await pub.PublishAsync("test.foo.bar.baz", "data");
 
         var result = await received.Task.WaitAsync(TimeSpan.FromSeconds(5));
-        Assert.Equal("test.foo.bar.baz", result);
+        result.ShouldBe("test.foo.bar.baz");
     }
 
     [Fact]
@@ -163,8 +164,8 @@ public class IntegrationTests : IAsyncDisposable
         await pub.PublishAsync("fanout", "hello");
 
         await done.Task.WaitAsync(TimeSpan.FromSeconds(5));
-        Assert.Equal(1, count1);
-        Assert.Equal(1, count2);
+        count1.ShouldBe(1);
+        count2.ShouldBe(1);
     }
 
     [Fact]