feat(CS-P2): registration fee (zen) + already-registered guard on Guardsman

src/GameLogic/CastleSiege/CastleSiegeConfiguration.cs

@@ -25,6 +25,12 @@ public class CastleSiegeConfiguration
     /// <summary>Gets or sets how long the siege phase lasts.</summary>
     public TimeSpan SiegeDuration { get; set; } = TimeSpan.FromMinutes(10);
 
+    /// <summary>
+    /// Gets or sets the registration fee (in zen) a guild master must pay to register the guild
+    /// for the siege. 0 disables the fee.
+    /// </summary>
+    public int RegistrationFee { get; set; } = 100000;
+
     /// <summary>
     /// Returns true if <paramref name="now"/> falls within a 5-second window of any configured
     /// registration-open time.