feat(CS-P1): periodic Castle Siege plugin (per-context tick + custom config)

src/GameLogic/PlugIns/PeriodicTasks/CastleSiegeEventPlugIn.cs

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+// <copyright file="CastleSiegeEventPlugIn.cs" company="MUnique">
+// Licensed under the MIT License. See LICENSE file in the project root for full license information.
+// </copyright>
+
+namespace MUnique.OpenMU.GameLogic.PlugIns.PeriodicTasks;
+
+using System.Collections.Concurrent;
+using System.Runtime.InteropServices;
+using MUnique.OpenMU.GameLogic.CastleSiege;
+using MUnique.OpenMU.PlugIns;
+
+/// <summary>
+/// Drives the Castle Siege phase state machine: ticks it every second and carries its configuration.
+/// State is per-<see cref="IGameContext"/> and kept in memory (P1: no persistence).
+/// </summary>
+[PlugIn]
+[Display(Name = nameof(CastleSiegeEventPlugIn), Description = "Castle Siege event (P1 skeleton: phase state machine + scheduling).")]
+[Guid("6E2C8B41-9A4D-4C2E-9E7B-1F2A3B4C5D60")]
+public sealed class CastleSiegeEventPlugIn : IPeriodicTaskPlugIn, ISupportCustomConfiguration<CastleSiegeConfiguration>, ISupportDefaultCustomConfiguration
+{
+    private static readonly ConcurrentDictionary<IGameContext, CastleSiegeContext> Contexts = new();
+
+    /// <inheritdoc />
+    public CastleSiegeConfiguration? Configuration { get; set; }
+
+    /// <summary>
+    /// Gets the Castle Siege context for a game context, if the periodic tick has initialized it.
+    /// </summary>
+    /// <param name="gameContext">The game context.</param>
+    /// <returns>The context, or <c>null</c> if not yet initialized.</returns>
+    /// <remarks>Static so GM chat commands can reach the state machine without a plugin instance
+    /// (<c>GetKnownPlugInsOf</c> returns Types, not instances). The tick runs every second, so the
+    /// context exists within ~1s of server start.</remarks>
+    public static CastleSiegeContext? TryGetContext(IGameContext gameContext)
+        => Contexts.TryGetValue(gameContext, out var context) ? context : null;
+
+    /// <inheritdoc />
+    public object CreateDefaultConfig() => new CastleSiegeConfiguration();
+
+    /// <inheritdoc />
+    public async ValueTask ExecuteTaskAsync(GameContext gameContext)
+    {
+        var context = Contexts.GetOrAdd(gameContext, _ => new CastleSiegeContext(this.Configuration ?? new CastleSiegeConfiguration()));
+        await context.TickAsync(DateTime.UtcNow).ConfigureAwait(false);
+    }
+
+    /// <inheritdoc />
+    public void ForceStart()
+    {
+        // Force-start applies to every active game context's siege.
+        foreach (var context in Contexts.Values)
+        {
+            _ = context.ForceStartRegistrationAsync(DateTime.UtcNow);
+        }
+    }
+}