Merge branch 'feature/core-lifecycle' into main

Reconcile close reason tracking: feature branch's MarkClosed() and
ShouldSkipFlush/FlushAndCloseAsync now use main's ClientClosedReason
enum. ClosedState enum retained for forward compatibility.

src/NATS.Server/NatsOptions.cs

@@ -38,6 +38,18 @@ public sealed class NatsOptions
     // 0 = disabled
     public int MonitorHttpsPort { get; set; }
 
+    // Lifecycle / lame-duck mode
+    public TimeSpan LameDuckDuration { get; set; } = TimeSpan.FromMinutes(2);
+    public TimeSpan LameDuckGracePeriod { get; set; } = TimeSpan.FromSeconds(10);
+
+    // File paths
+    public string? PidFile { get; set; }
+    public string? PortsFileDir { get; set; }
+    public string? ConfigFile { get; set; }
+
+    // Profiling (0 = disabled)
+    public int ProfPort { get; set; }
+
     // TLS
     public string? TlsCert { get; set; }
     public string? TlsKey { get; set; }