feat(CS): castle flag owner logo (C1 B9 02) + catapults for war atmosphere

#1 Castle flags now show the owner guild's logo: resolve owner name -> guild logo
(cached), broadcast C1 B9 02 (32-byte mark) to players on the castle map every 15s.
#3 War atmosphere: spawn catapult NPCs 221/222 at siege start (client renders them
as siege weapons); the 0xB2/0x17 start flag already flips the map to warzone mode.
All raw S6 packets, no client changes.

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

src/GameServer/RemoteView/CastleSiege/CastleSiegeStatusViewPlugIn.cs

@@ -75,4 +75,30 @@ public class CastleSiegeStatusViewPlugIn : ICastleSiegeStatusViewPlugIn
 
         await connection.SendAsync(WritePacket).ConfigureAwait(false);
     }
+
+    /// <inheritdoc />
+    public async ValueTask SetCastleFlagAsync(ReadOnlyMemory<byte> guildLogo)
+    {
+        var connection = this._player.Connection;
+        if (connection is null)
+        {
+            return;
+        }
+
+        int WritePacket()
+        {
+            // C1 24 B9 02 <32-byte guild logo>
+            var span = connection.Output.GetSpan(36)[..36];
+            span.Clear();
+            span[0] = 0xC1;
+            span[1] = 0x24;
+            span[2] = 0xB9;
+            span[3] = 0x02;
+            var logo = guildLogo.Span;
+            logo[..Math.Min(32, logo.Length)].CopyTo(span.Slice(4, 32));
+            return span.Length;
+        }
+
+        await connection.SendAsync(WritePacket).ConfigureAwait(false);
+    }
 }