Build initial MCP SSH server

src/McpSsh.Server/Terminal/TerminalConnection.cs

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+using Renci.SshNet;
+using Renci.SshNet.Common;
+using McpSsh.Server.Ssh;
+
+namespace McpSsh.Server.Terminal;
+
+public interface ITerminalConnection : IDisposable
+{
+    bool DataAvailable { get; }
+
+    string ReadAvailable();
+
+    void Write(string input);
+}
+
+public interface ITerminalConnectionFactory
+{
+    ITerminalConnection Create(TerminalStartRequest request);
+}
+
+public sealed class SshNetTerminalConnectionFactory : ITerminalConnectionFactory
+{
+    private const int ShellBufferSize = 16 * 1024;
+    private readonly ISshKeyResolver _keyResolver;
+
+    public SshNetTerminalConnectionFactory(ISshKeyResolver keyResolver)
+    {
+        _keyResolver = keyResolver;
+    }
+
+    public ITerminalConnection Create(TerminalStartRequest request)
+    {
+        try
+        {
+            var keyPath = _keyResolver.ResolveKeyPath(request.KeyPath);
+            var keyFile = string.IsNullOrEmpty(request.KeyPassphrase)
+                ? new PrivateKeyFile(keyPath)
+                : new PrivateKeyFile(keyPath, request.KeyPassphrase);
+            var client = new SshClient(request.Host, request.Port, request.Username, keyFile);
+
+            client.Connect();
+
+            var stream = client.CreateShellStream(
+                "xterm-256color",
+                (uint)request.Cols,
+                (uint)request.Rows,
+                width: 0,
+                height: 0,
+                bufferSize: ShellBufferSize);
+
+            return new SshNetTerminalConnection(client, stream, keyFile);
+        }
+        catch (SshAuthenticationException ex)
+        {
+            throw new SshToolException("ssh_authentication_failed", "SSH key authentication failed. Check the username, key path, and key passphrase.", ex);
+        }
+        catch (SshException ex)
+        {
+            throw new SshToolException("ssh_error", ex.Message, ex);
+        }
+    }
+
+    private sealed class SshNetTerminalConnection : ITerminalConnection
+    {
+        private readonly SshClient _client;
+        private readonly ShellStream _stream;
+        private readonly PrivateKeyFile _keyFile;
+
+        public SshNetTerminalConnection(SshClient client, ShellStream stream, PrivateKeyFile keyFile)
+        {
+            _client = client;
+            _stream = stream;
+            _keyFile = keyFile;
+        }
+
+        public bool DataAvailable => _stream.DataAvailable;
+
+        public string ReadAvailable()
+        {
+            return _stream.Read();
+        }
+
+        public void Write(string input)
+        {
+            _stream.Write(input);
+        }
+
+        public void Dispose()
+        {
+            _stream.Dispose();
+            _client.Dispose();
+            _keyFile.Dispose();
+        }
+    }
+}