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>

src/GameLogic/CastleSiege/CastleSiegeThroneCaptureTalkPlugIn.cs

@@ -65,17 +65,34 @@ public class CastleSiegeThroneCaptureTalkPlugIn : IPlayerTalkToNpcPlugIn
             return;
         }
 
-        var (success, reason) = context.TryCaptureThrone(guildName);
-        if (success)
+        // The throne is taken by holding the Crown, not by talking here — give guidance based on the state.
+        await ShowAsync(player, DescribeThroneStep(context, guildName)).ConfigureAwait(false);
+    }
+
+    private static string DescribeThroneStep(CastleSiegeContext context, string guildName)
+    {
+        if (context.Phase != CastleSiegePhase.Siege)
         {
-            await player.GameContext.ForEachPlayerAsync(p =>
-                p.InvokeViewPlugInAsync<IShowMessagePlugIn>(v =>
-                    v.ShowMessageAsync($"Guild '{guildName}' has CAPTURED THE THRONE! They will win the castle if they hold it until the siege ends.", MessageType.GoldenCenter)).AsTask()).ConfigureAwait(false);
+            return "The siege is not running yet.";
         }
-        else
+
+        if (context.DefensesRemaining > 0)
         {
-            await ShowAsync(player, reason).ConfigureAwait(false);
+            return $"Destroy all castle gates first ({context.DefensesRemaining} remaining), then hold both Crown Switches.";
         }
+
+        var eligible = context.GetShieldEligibleGuild();
+        if (eligible is null)
+        {
+            return "All gates are down! Hold BOTH Crown Switches with your guild — the Crown's shield will drop.";
+        }
+
+        if (eligible == guildName)
+        {
+            return "Your guild holds both switches and the shield is down — send your GUILD MASTER to hold the Crown to take the throne!";
+        }
+
+        return $"Guild '{eligible}' is holding both switches. Take a switch back to raise their shield.";
     }
 
     private static ValueTask ShowAsync(Player player, string text)