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/ClientTests.cs

@@ -3,6 +3,8 @@ using System.Net;
 using System.Net.Sockets;
 using System.Text;
 using System.Text.Json;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Logging.Abstractions;
 using NATS.Server;
 using NATS.Server.Protocol;
 
@@ -37,7 +39,7 @@ public class ClientTests : IAsyncDisposable
             Port = 4222,
         };
 
-        _natsClient = new NatsClient(1, _serverSocket, new NatsOptions(), serverInfo);
+        _natsClient = new NatsClient(1, _serverSocket, new NatsOptions(), serverInfo, NullLogger.Instance);
     }
 
     public async ValueTask DisposeAsync()
@@ -57,9 +59,9 @@ public class ClientTests : IAsyncDisposable
         var n = await _clientSocket.ReceiveAsync(buf, SocketFlags.None);
         var response = Encoding.ASCII.GetString(buf, 0, n);
 
-        Assert.StartsWith("INFO ", response);
-        Assert.Contains("server_id", response);
-        Assert.Contains("\r\n", response);
+        response.ShouldStartWith("INFO ");
+        response.ShouldContain("server_id");
+        response.ShouldContain("\r\n");
 
         await _cts.CancelAsync();
     }
@@ -80,7 +82,7 @@ public class ClientTests : IAsyncDisposable
         var n = await _clientSocket.ReceiveAsync(buf, SocketFlags.None);
         var response = Encoding.ASCII.GetString(buf, 0, n);
 
-        Assert.Contains("PONG\r\n", response);
+        response.ShouldContain("PONG\r\n");
 
         await _cts.CancelAsync();
     }