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.

src/GameLogic/CastleSiege/CastleSiegeGuardsmanTalkPlugIn.cs

@@ -65,8 +65,23 @@ public class CastleSiegeGuardsmanTalkPlugIn : IPlayerTalkToNpcPlugIn
             }
         }
 
+        if (context.RegisteredGuilds.Contains(guildName))
+        {
+            await ShowAsync(player, $"Your guild '{guildName}' is already registered for the Castle Siege.").ConfigureAwait(false);
+            return;
+        }
+
+        var fee = context.Configuration.RegistrationFee;
+        if (fee > 0 && !player.TryRemoveMoney(fee))
+        {
+            await ShowAsync(player, $"You need {fee} zen to register your guild for the Castle Siege.").ConfigureAwait(false);
+            return;
+        }
+
         context.RegisterGuild(guildName);
-        await ShowAsync(player, $"Your guild '{guildName}' is registered for the Castle Siege.").ConfigureAwait(false);
+        await ShowAsync(player, fee > 0
+            ? $"Your guild '{guildName}' is registered for the Castle Siege. ({fee} zen paid)"
+            : $"Your guild '{guildName}' is registered for the Castle Siege.").ConfigureAwait(false);
     }
 
     private static ValueTask ShowAsync(Player player, string text)