feat(hs): HeykelSavasiContext team tracking + balance rule

Adds the HeykelSavasiTeam enum (None/Red/Blue) and the HeykelSavasiContext
skeleton (subclass of MiniGameContext) with team registration
(AssignTeam/GetTeam/PlayersOf/TeamCount) and a join-balance rule
(|Red-Blue| <= 2 after the prospective join), exposed as a pure static
IsJoinAllowed for fast unit testing without constructing the full context.

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

tests/MUnique.OpenMU.Tests/HeykelSavasi/HeykelSavasiContextTests.cs

@@ -0,0 +1,37 @@
+// <copyright file="HeykelSavasiContextTests.cs" company="MUnique">
+// Licensed under the MIT License. See LICENSE file in the project root for full license information.
+// </copyright>
+
+namespace MUnique.OpenMU.Tests.HeykelSavasi;
+
+using MUnique.OpenMU.GameLogic.MiniGames;
+
+/// <summary>
+/// Tests for the Heykel Savasi team-balance rule.
+/// </summary>
+/// <remarks>
+/// <see cref="HeykelSavasiContext"/> derives from <see cref="MiniGameContext"/>, whose constructor
+/// creates a map and launches a background game loop via <c>Task.Run</c>. Constructing a full context
+/// is impractical in a fast unit test, so the balance decision is exposed as a pure static method,
+/// <see cref="HeykelSavasiContext.IsJoinAllowed"/>, and tested directly against it.
+/// </remarks>
+[TestFixture]
+public class HeykelSavasiContextTests
+{
+    [Test]
+    public void BalanceRule_BlocksJoinWhenDifferenceWouldExceedTwo()
+    {
+        // Red 0, Blue 0 -> either team may be joined.
+        Assert.That(HeykelSavasiContext.IsJoinAllowed(0, 0, HeykelSavasiTeam.Red), Is.True);
+
+        // Red already has 2, Blue has 0. Adding a 3rd to Red would make the difference 3.
+        Assert.That(HeykelSavasiContext.IsJoinAllowed(2, 0, HeykelSavasiTeam.Red), Is.False, "2-0 iken Red'e katilim farki 3 yapar");
+        Assert.That(HeykelSavasiContext.IsJoinAllowed(2, 0, HeykelSavasiTeam.Blue), Is.True);
+    }
+
+    [Test]
+    public void BalanceRule_NoneTeamIsNeverJoinable()
+    {
+        Assert.That(HeykelSavasiContext.IsJoinAllowed(0, 0, HeykelSavasiTeam.None), Is.False);
+    }
+}