feat(CS): run the siege on ONE designated server (CastleSiegeServerId)

With multiple game servers each has its own map instances, so the siege ran
independently on all of them - a guild could win uncontested on an empty server's
Valley of Loren. Now the siege (tick/spawn/battle/registration) runs only on the
server whose Id == config.CastleSiegeServerId (AdminPanel-editable). Other servers
skip the siege and just mirror the shared castle owner from config so the hunting-map
gate + castle flag rewards still work everywhere. The Guardsman on non-siege servers
tells players which server to switch to.

src/GameLogic/CastleSiege/CastleSiegeContext.cs

@@ -158,6 +158,16 @@ public class CastleSiegeContext
         this._dirty = true;
     }
 
+    /// <summary>
+    /// Mirrors the shared castle owner from the configuration. Used on game servers that do NOT host the
+    /// siege, so their hunting-map gate and castle flag still reflect the current owner. Does not mark the
+    /// state dirty (these servers never persist).
+    /// </summary>
+    public void SyncOwnerFromConfig()
+    {
+        this.OwnerGuildName = this.Configuration.PersistedOwnerGuildName;
+    }
+
     /// <summary>
     /// Sets the weekly auto-schedule (days of week + UTC time) into the configuration and marks the state
     /// dirty for persistence. Empty days disables auto-start (manual only). The configuration is the single