feat(CS-P4): castle-exclusive hunting map (Land of Trials 31) gated to owner guild

Ownership reward: only members of the current castle-owning guild may warp into
Land of Trials (map 31); sealed while unowned; GMs bypass. Enforced in both
WarpAction and WarpGateAction (// ADAMU-CUSTOM). Tax system deferred per user.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/GameLogic/CastleSiege/CastleSiegeMapAccess.cs

@@ -0,0 +1,75 @@
+// <copyright file="CastleSiegeMapAccess.cs" company="MUnique">
+// Licensed under the MIT License. See LICENSE file in the project root for full license information.
+// </copyright>
+
+namespace MUnique.OpenMU.GameLogic.CastleSiege;
+
+using MUnique.OpenMU.DataModel.Entities;
+using MUnique.OpenMU.GameLogic.PlugIns.PeriodicTasks;
+using MUnique.OpenMU.Interfaces;
+
+/// <summary>
+/// ADAMU-CUSTOM (Castle Siege P4 — ownership reward): gates entry to the castle-exclusive hunting map
+/// (Land of Trials, map 31). Only members of the current castle-owning guild may enter; while the castle
+/// has no owner the map stays sealed. Game masters always pass (admin/testing).
+/// </summary>
+public static class CastleSiegeMapAccess
+{
+    /// <summary>The castle-exclusive hunting map number (Land of Trials).</summary>
+    public const short CastleHuntingMapNumber = 31;
+
+    /// <summary>
+    /// Checks whether the player may enter the given map. Only the castle hunting map (31) is restricted;
+    /// every other map is always allowed.
+    /// </summary>
+    /// <param name="player">The player attempting to enter.</param>
+    /// <param name="mapNumber">The target map number.</param>
+    /// <returns>Whether entry is allowed and, when not, a human-readable reason to show the player.</returns>
+    public static async ValueTask<(bool Allowed, string? Error)> CanEnterMapAsync(Player player, short mapNumber)
+    {
+        if (mapNumber != CastleHuntingMapNumber)
+        {
+            return (true, null);
+        }
+
+        // Game masters may always enter (admin/testing).
+        if (player.SelectedCharacter?.CharacterStatus >= CharacterStatus.GameMaster)
+        {
+            return (true, null);
+        }
+
+        var context = CastleSiegeEventPlugIn.TryGetContext(player.GameContext);
+        var owner = context?.OwnerGuildName;
+        if (string.IsNullOrEmpty(owner))
+        {
+            return (false, "The castle hunting ground is sealed until a guild owns the castle.");
+        }
+
+        var guildName = await GetGuildNameAsync(player).ConfigureAwait(false);
+        if (guildName is not null && string.Equals(guildName, owner, StringComparison.Ordinal))
+        {
+            return (true, null);
+        }
+
+        return (false, $"Only members of the castle-owning guild '{owner}' may enter this hunting ground.");
+    }
+
+    private static async ValueTask<string?> GetGuildNameAsync(Player player)
+    {
+        if (player.GuildStatus is not { } guildStatus)
+        {
+            return null;
+        }
+
+        if (player.GameContext is IGameServerContext serverContext)
+        {
+            var guild = await serverContext.GuildServer.GetGuildAsync(guildStatus.GuildId).ConfigureAwait(false);
+            if (guild?.Name is { Length: > 0 } name)
+            {
+                return name;
+            }
+        }
+
+        return guildStatus.GuildId.ToString();
+    }
+}