feat(castle-siege): adopt the upstream Castle Siege data model and persistence

Brings in the database layer of upstream OpenMU PRs #754 and #860 without
touching AdaMu's working Castle Siege gameplay. This is purely additive: the
existing 5-phase implementation still runs exactly as before.

What is included:

- DataModel: CastleSiegeState (the original Season 6 values 0-9, which are
  exactly what the game client's CASTLESIEGE_STATE enum expects),
  CastleSiegeJoinSide, and the zone/NPC/upgrade definition types.
- Entities: CastleSiegeData, CastleSiegeGuildRegistration, CastleSiegeNpcState.
  These identify a guild by its persistent Guid rather than by name.
- Generated persistence: 8 BasicModel + 8 EntityFramework model classes,
  CastleSiegeExtensions, and the regenerated ExtendedTypeContext,
  MapsterConfigurator and GameConfiguration partials.
- Migrations: 20260730194321_AddCastleSiege and
  20260801162427_ConfigureCastleSiegePersistence, plus the model snapshot.
- EntityDataContext gains the two DbSets and the five model registrations.
- EntityFrameworkContextBase only publishes configuration changes for entities
  in the configuration schema, so siege state writes are no longer broadcast as
  configuration changes.

AdaMu-specific adaptations:

- UpdateVersion.AddCastleSiegeData is 105, not upstream's 100. AdaMu already
  ships 95-104, and the applied-update bookkeeping is keyed on this value, so a
  collision would skip or re-run updates on live databases.
- CastleSiegeInitializer does not seed a weekly StateSchedule. Upstream drives
  the cycle from a fixed Saturday schedule; AdaMu drives it manually from
  CastleSiegeEventPlugIn and the AdminPanel, so the schedule is left empty and
  nothing reads it.

The seeded NPC definitions match AdaMu's existing hard-coded coordinates
exactly (6 gates, the two crown switches and the crown), and additionally
provide 4 guardian statues, 6 guardsmen and real gate/statue hit point tables
that the current implementation does not have yet.

Two pre-existing migrations were restyled by upstream (copyright header, using
placement, trailing comma). No functional change.

Verified: full server build succeeds with 0 errors.

src/Persistence/Initialization/Updates/AddCastleSiegeDataUpdatePlugIn.cs

@@ -0,0 +1,59 @@
+// <copyright file="AddCastleSiegeDataUpdatePlugIn.cs" company="MUnique">
+// Licensed under the MIT License. See LICENSE file in the project root for full license information.
+// </copyright>
+
+namespace MUnique.OpenMU.Persistence.Initialization.Updates;
+
+using System.Runtime.InteropServices;
+using MUnique.OpenMU.DataModel.Configuration;
+using MUnique.OpenMU.DataModel.Entities;
+using MUnique.OpenMU.Persistence.Initialization.VersionSeasonSix.Events;
+using MUnique.OpenMU.PlugIns;
+
+/// <summary>
+/// Adds the Castle Siege configuration and persistent state to an existing Season 6 database.
+/// </summary>
+[PlugIn]
+[Display(Name = PlugInName, Description = PlugInDescription)]
+[Guid("CD201E33-37C9-4C85-95CC-16042B28E974")]
+public class AddCastleSiegeDataUpdatePlugIn : UpdatePlugInBase
+{
+    /// <summary>
+    /// The plug-in name.
+    /// </summary>
+    internal const string PlugInName = "Add Castle Siege data";
+
+    /// <summary>
+    /// The plug-in description.
+    /// </summary>
+    internal const string PlugInDescription = "This update adds the Castle Siege configuration and persistent state.";
+
+    /// <inheritdoc />
+    public override string Name => PlugInName;
+
+    /// <inheritdoc />
+    public override string Description => PlugInDescription;
+
+    /// <inheritdoc />
+    public override UpdateVersion Version => UpdateVersion.AddCastleSiegeData;
+
+    /// <inheritdoc />
+    public override string DataInitializationKey => VersionSeasonSix.DataInitialization.Id;
+
+    /// <inheritdoc />
+    public override bool IsMandatory => true;
+
+    /// <inheritdoc />
+    public override DateTime CreatedAt => new(2026, 07, 28, 20, 0, 0, DateTimeKind.Utc);
+
+    /// <inheritdoc />
+    protected override async ValueTask ApplyAsync(IContext context, GameConfiguration gameConfiguration)
+    {
+        var initializer = new CastleSiegeInitializer(context, gameConfiguration);
+        var configuration = initializer.InitializeConfiguration();
+        if (!(await context.GetAsync<CastleSiegeData>().ConfigureAwait(false)).Any())
+        {
+            initializer.InitializeData(configuration);
+        }
+    }
+}