feat(CS): on-map siege countdown timer (S6 client protocol C1 B2 17/1E)

Client already renders the siege-map countdown but never received the packets.
New ICastleSiegeStatusViewPlugIn + RemoteView impl send the raw S6 packets:
C1 B2 17 (battle start/stop flag, arms the countdown) and C1 B2 1E (remaining
hour/minute). CastleSiegeEventPlugIn broadcasts them to players on the battle map
every 10s during Siege and sends stop at Settlement. No client changes. +1 test.

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

src/GameLogic/Views/CastleSiege/ICastleSiegeStatusViewPlugIn.cs

@@ -0,0 +1,25 @@
+// <copyright file="ICastleSiegeStatusViewPlugIn.cs" company="MUnique">
+// Licensed under the MIT License. See LICENSE file in the project root for full license information.
+// </copyright>
+
+namespace MUnique.OpenMU.GameLogic.Views.CastleSiege;
+
+/// <summary>
+/// Interface of a view which drives the client's on-map Castle Siege countdown (Season 6 protocol
+/// C1 B2 17 = battle start/stop flag, C1 B2 1E = remaining hour/minute).
+/// </summary>
+public interface ICastleSiegeStatusViewPlugIn : IViewPlugIn
+{
+    /// <summary>
+    /// Sends the siege battle start/stop flag (C1 B2 17). The client only ticks its countdown while this is set.
+    /// </summary>
+    /// <param name="started">Whether the siege battle is running.</param>
+    ValueTask SetBattleStateAsync(bool started);
+
+    /// <summary>
+    /// Sends the remaining siege time as hour/minute (C1 B2 1E) to (re)seed the countdown.
+    /// </summary>
+    /// <param name="hour">The remaining hours.</param>
+    /// <param name="minute">The remaining minutes.</param>
+    ValueTask SetTimerAsync(byte hour, byte minute);
+}