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/DataModel/Configuration/CastleSiegeNpcDefinition.cs

@@ -0,0 +1,55 @@
+// <copyright file="CastleSiegeNpcDefinition.cs" company="MUnique">
+// Licensed under the MIT License. See LICENSE file in the project root for full license information.
+// </copyright>
+
+namespace MUnique.OpenMU.DataModel.Configuration;
+
+using MUnique.OpenMU.Annotations;
+
+/// <summary>
+/// Defines a castle siege NPC instance, including its spawn location, side, and persistence settings.
+/// </summary>
+[Cloneable]
+public partial class CastleSiegeNpcDefinition
+{
+    /// <summary>
+    /// Gets or sets the monster definition template for this NPC.
+    /// </summary>
+    public virtual MonsterDefinition? MonsterDefinition { get; set; }
+
+    /// <summary>
+    /// Gets or sets the unique instance identifier within its NPC type.
+    /// </summary>
+    public byte InstanceId { get; set; }
+
+    /// <summary>
+    /// Gets or sets a value indicating whether this NPC's state is persisted to the database between sieges.
+    /// </summary>
+    public bool IsPersistedToDatabase { get; set; }
+
+    /// <summary>
+    /// Gets or sets the default join side this NPC belongs to.
+    /// </summary>
+    public CastleSiegeJoinSide DefaultSide { get; set; }
+
+    /// <summary>
+    /// Gets or sets the X coordinate of the NPC's spawn position.
+    /// </summary>
+    public byte SpawnX { get; set; }
+
+    /// <summary>
+    /// Gets or sets the Y coordinate of the NPC's spawn position.
+    /// </summary>
+    public byte SpawnY { get; set; }
+
+    /// <summary>
+    /// Gets or sets the facing direction of the NPC at spawn.
+    /// </summary>
+    public Direction Direction { get; set; }
+
+    /// <inheritdoc />
+    public override string ToString()
+    {
+        return $"{this.MonsterDefinition} #{this.InstanceId} at ({this.SpawnX},{this.SpawnY})";
+    }
+}