fix(CS): stop crown re-capture loop + show seal panel only to the master

- The occupier can no longer re-register its own throne (canCapture = eligible != occupier),
  which caused a repeating 60s panel loop; only a DIFFERENT guild can contest.
- The 60s registration panel (0xB2/0x15) is now sent ONLY to the master on the crown,
  not broadcast to switch-holders/other players. Shield(0x16) + capture(0x18) still broadcast.
+1 test (15 total).

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

@@ -236,6 +236,35 @@ public class CastleSiegeContextTest
         Assert.That(ctx.OccupierGuildName, Is.Null);
     }
 
+    /// <summary>Tests that the occupier can't re-capture its own throne, but a different guild can contest it.</summary>
+    [Test]
+    public async Task OccupierDoesNotRecaptureButAnotherGuildCanContestAsync()
+    {
+        var ctx = new CastleSiegeContext(Config());
+        await ctx.ForceStartRegistrationAsync(T0);
+        await ctx.ForcePhaseAsync(CastleSiegePhase.Siege, T0);
+        ctx.SetDefenseCount(0);
+        var hold = TimeSpan.FromSeconds(60);
+
+        ctx.SetSwitchHolder(217, "A");
+        ctx.SetSwitchHolder(218, "A");
+        ctx.TickCrownHold("A", true, T0, hold);
+        Assert.That(ctx.TickCrownHold("A", true, T0.AddSeconds(60), hold).Event, Is.EqualTo(CrownEvent.Captured));
+        Assert.That(ctx.OccupierGuildName, Is.EqualTo("A"));
+
+        // A keeps holding — no re-registration loop, but the shield stays down (they hold it).
+        var after = ctx.TickCrownHold("A", true, T0.AddSeconds(61), hold);
+        Assert.That(after.Event, Is.EqualTo(CrownEvent.None));
+        Assert.That(after.ShieldDown, Is.True);
+
+        // B takes both switches and can contest/capture.
+        ctx.SetSwitchHolder(217, "B");
+        ctx.SetSwitchHolder(218, "B");
+        Assert.That(ctx.TickCrownHold("B", true, T0.AddSeconds(62), hold).Event, Is.EqualTo(CrownEvent.HoldStarted));
+        Assert.That(ctx.TickCrownHold("B", true, T0.AddSeconds(122), hold).Event, Is.EqualTo(CrownEvent.Captured));
+        Assert.That(ctx.OccupierGuildName, Is.EqualTo("B"));
+    }
+
     private static CastleSiegeConfiguration Config() => new()
     {
         RegistrationDuration = TimeSpan.FromMinutes(5),