feat(CS): persist owner/phase/registrations across restarts via plugin config JSON

Castle Siege state was in-memory, so the castle owner (and thus the P4 hunting-map
reward) reset on every server restart/redeploy. Now the context marks itself dirty
on any persistable change (phase transition, registration, owner set); the plugin's
periodic tick writes a snapshot into its own PlugInConfiguration CustomConfiguration
(a JSON blob already stored in PostgreSQL - no schema migration) and restores it on
startup. Battle state (defenses/switches/occupier) stays transient. +2 unit tests.

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

tests/MUnique.OpenMU.Tests/CastleSiege/CastleSiegeContextTest.cs

@@ -123,6 +123,41 @@ public class CastleSiegeContextTest
         Assert.That(ctx.OccupierGuildName, Is.Null);
     }
 
+    /// <summary>Tests that restoring persisted state sets phase/owner/registrations without raising PhaseChanged.</summary>
+    [Test]
+    public void RestoreStateSetsStateWithoutFiringPhaseChanged()
+    {
+        var ctx = new CastleSiegeContext(Config());
+        var phaseChangedFired = false;
+        ctx.PhaseChanged += _ => phaseChangedFired = true;
+
+        ctx.RestoreState("Winners", CastleSiegePhase.Ownership, T0, new[] { "Winners", "Losers" });
+
+        Assert.That(ctx.Phase, Is.EqualTo(CastleSiegePhase.Ownership));
+        Assert.That(ctx.OwnerGuildName, Is.EqualTo("Winners"));
+        Assert.That(ctx.RegisteredGuilds, Is.EquivalentTo(new[] { "Winners", "Losers" }));
+        Assert.That(phaseChangedFired, Is.False);
+        Assert.That(ctx.ConsumeDirty(), Is.False, "restore must not mark the state dirty");
+    }
+
+    /// <summary>Tests that state-changing operations flip the dirty flag, which ConsumeDirty reads-and-resets.</summary>
+    [Test]
+    public async Task DirtyFlagTracksPersistableChangesAsync()
+    {
+        var ctx = new CastleSiegeContext(Config());
+        Assert.That(ctx.ConsumeDirty(), Is.False, "a fresh context has nothing to persist");
+
+        await ctx.ForceStartRegistrationAsync(T0); // phase transition -> dirty
+        Assert.That(ctx.ConsumeDirty(), Is.True);
+        Assert.That(ctx.ConsumeDirty(), Is.False, "ConsumeDirty resets the flag");
+
+        ctx.RegisterGuild("Attackers"); // registration -> dirty
+        Assert.That(ctx.ConsumeDirty(), Is.True);
+
+        ctx.SetOwner("Attackers"); // owner change -> dirty
+        Assert.That(ctx.ConsumeDirty(), Is.True);
+    }
+
     private static CastleSiegeConfiguration Config() => new()
     {
         RegistrationDuration = TimeSpan.FromMinutes(5),