Build initial MCP SSH server

tests/McpSsh.Tests/JsonLineAuditLoggerTests.cs

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+using System.Text.Json;
+using McpSsh.Server.Audit;
+
+namespace McpSsh.Tests;
+
+public sealed class JsonLineAuditLoggerTests
+{
+    [Fact]
+    public void Log_WritesJsonLineAndRedactsSensitiveMarkers()
+    {
+        using var writer = new StringWriter();
+        var logger = new JsonLineAuditLogger(writer);
+
+        logger.Log(new AuditEvent(
+            DateTimeOffset.Parse("2026-05-24T12:00:00Z"),
+            "ssh_exec",
+            "prod-api",
+            "deploy",
+            "echo token=abc123",
+            Success: true,
+            DurationMs: 42));
+
+        using var document = JsonDocument.Parse(writer.ToString());
+        var root = document.RootElement;
+
+        Assert.Equal("ssh_exec", root.GetProperty("tool").GetString());
+        Assert.Equal("prod-api", root.GetProperty("host").GetString());
+        Assert.Equal("echo token=***", root.GetProperty("command").GetString());
+        Assert.True(root.GetProperty("success").GetBoolean());
+    }
+}