feat(CS): authentic Crown-hold throne capture (S6 protocol) replacing Sinior-talk

Break all gates + hold both switches (defenses down) -> the Crown shield drops
(C1 B2 16=0). The guild master then stands on the Crown (176,212) and holds for
CrownHoldDuration (default 60s, client shows a 60s countdown via C1 B2 15) to
capture; capture broadcasts C1 B2 18 + golden text and sets the occupier. Losing a
switch or leaving the crown resets the hold (contestable until the siege timer ends).
Sinior (223) is now informational guidance. +2 tests (14 total).

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

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

@@ -193,6 +193,49 @@ public class CastleSiegeContextTest
         Assert.That(ctx.GetRemainingSiegeTime(T0.AddMinutes(15)), Is.EqualTo(TimeSpan.Zero), "past the end -> clamped to zero");
     }
 
+    /// <summary>Tests that a guild master holding the crown (both switches held, defenses down) captures after the hold duration.</summary>
+    [Test]
+    public async Task CrownHoldCapturesAfterHoldDurationAsync()
+    {
+        var ctx = new CastleSiegeContext(Config());
+        await ctx.ForceStartRegistrationAsync(T0);
+        await ctx.ForcePhaseAsync(CastleSiegePhase.Siege, T0);
+        ctx.SetDefenseCount(0);
+        ctx.SetSwitchHolder(217, "Attackers");
+        ctx.SetSwitchHolder(218, "Attackers");
+        Assert.That(ctx.GetShieldEligibleGuild(), Is.EqualTo("Attackers"));
+
+        var hold = TimeSpan.FromSeconds(60);
+        Assert.That(ctx.TickCrownHold("Attackers", true, T0, hold).Event, Is.EqualTo(CrownEvent.HoldStarted));
+        Assert.That(ctx.TickCrownHold("Attackers", true, T0.AddSeconds(30), hold).Event, Is.EqualTo(CrownEvent.None));
+        Assert.That(ctx.OccupierGuildName, Is.Null);
+
+        var captured = ctx.TickCrownHold("Attackers", true, T0.AddSeconds(60), hold);
+        Assert.That(captured.Event, Is.EqualTo(CrownEvent.Captured));
+        Assert.That(captured.ShieldDown, Is.True);
+        Assert.That(ctx.OccupierGuildName, Is.EqualTo("Attackers"));
+    }
+
+    /// <summary>Tests that losing a switch mid-hold resets the crown-hold progress (contestable).</summary>
+    [Test]
+    public async Task CrownHoldResetsWhenSwitchLostAsync()
+    {
+        var ctx = new CastleSiegeContext(Config());
+        await ctx.ForceStartRegistrationAsync(T0);
+        await ctx.ForcePhaseAsync(CastleSiegePhase.Siege, T0);
+        ctx.SetDefenseCount(0);
+        ctx.SetSwitchHolder(217, "A");
+        ctx.SetSwitchHolder(218, "A");
+
+        Assert.That(ctx.TickCrownHold("A", true, T0, TimeSpan.FromSeconds(60)).Event, Is.EqualTo(CrownEvent.HoldStarted));
+
+        ctx.SetSwitchHolder(218, null); // lost a switch -> no longer eligible
+        var reset = ctx.TickCrownHold(ctx.GetShieldEligibleGuild(), false, T0.AddSeconds(10), TimeSpan.FromSeconds(60));
+        Assert.That(reset.ShieldDown, Is.False);
+        Assert.That(reset.Event, Is.EqualTo(CrownEvent.HoldReset));
+        Assert.That(ctx.OccupierGuildName, Is.Null);
+    }
+
     private static CastleSiegeConfiguration Config() => new()
     {
         RegistrationDuration = TimeSpan.FromMinutes(5),