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>

src/GameLogic/CastleSiege/CastleSiegeContext.cs

@@ -22,6 +22,7 @@ public class CastleSiegeContext
     private DateTime _phaseStartedUtc;
     private string? _occupier;
     private int _defensesRemaining;
+    private bool _dirty;
 
     /// <summary>Initializes a new instance of the <see cref="CastleSiegeContext"/> class.</summary>
     /// <param name="configuration">The cycle timing configuration.</param>
@@ -40,6 +41,9 @@ public class CastleSiegeContext
     /// <summary>Gets the current phase.</summary>
     public CastleSiegePhase Phase { get; private set; }
 
+    /// <summary>Gets the UTC time the current phase started (used for persistence/restore).</summary>
+    public DateTime PhaseStartedUtc => this._phaseStartedUtc;
+
     /// <summary>Gets the current owner guild name, or null if unowned.</summary>
     public string? OwnerGuildName { get; private set; }
 
@@ -134,12 +138,50 @@ public class CastleSiegeContext
             && !this._registeredGuilds.Contains(guildName))
         {
             this._registeredGuilds.Add(guildName);
+            this._dirty = true;
         }
     }
 
     /// <summary>Admin: sets (or clears) the current owner guild name.</summary>
     /// <param name="guildName">The owner guild name, or null to clear.</param>
-    public void SetOwner(string? guildName) => this.OwnerGuildName = guildName;
+    public void SetOwner(string? guildName)
+    {
+        this.OwnerGuildName = guildName;
+        this._dirty = true;
+    }
+
+    /// <summary>
+    /// Returns whether the persistable state changed since the last call, resetting the flag.
+    /// Called each tick by the plugin to decide whether to write state to the database.
+    /// </summary>
+    public bool ConsumeDirty()
+    {
+        var dirty = this._dirty;
+        this._dirty = false;
+        return dirty;
+    }
+
+    /// <summary>
+    /// Restores persisted state on startup (owner, phase, phase-start, registrations) directly, without
+    /// firing <see cref="PhaseChanged"/> or marking the state dirty. Battle state stays cleared.
+    /// </summary>
+    /// <param name="owner">The persisted owner guild name, or null.</param>
+    /// <param name="phase">The persisted phase.</param>
+    /// <param name="phaseStartedUtc">When the persisted phase started (UTC), or null to keep the default.</param>
+    /// <param name="registeredGuilds">The persisted registered guild names, or null.</param>
+    public void RestoreState(string? owner, CastleSiegePhase phase, DateTime? phaseStartedUtc, IEnumerable<string>? registeredGuilds)
+    {
+        this.OwnerGuildName = owner;
+        this.Phase = phase;
+        this._phaseStartedUtc = phaseStartedUtc ?? this._phaseStartedUtc;
+        this._registeredGuilds.Clear();
+        if (registeredGuilds is not null)
+        {
+            this._registeredGuilds.AddRange(registeredGuilds);
+        }
+
+        this._dirty = false;
+    }
 
     /// <summary>Sets how many castle defenses (gates + guardian statues) exist this siege (when spawned).</summary>
     /// <param name="count">The defense count.</param>
@@ -222,6 +264,7 @@ public class CastleSiegeContext
     {
         this.Phase = phase;
         this._phaseStartedUtc = now;
+        this._dirty = true;
         this.PhaseChanged?.Invoke(phase);
         return ValueTask.CompletedTask;
     }