refactor: reorganize project structure and move examples

- Move examples (Blackjack, TicTacToe) to the root directory
- Convert example projects from Console applications to Libraries
- Add Directory.Build.props for shared build settings
- Update solution file and project references to reflect new paths

TicTacToe/Singletons/GameState.cs

@@ -0,0 +1,14 @@
+using MessagePack;
+
+namespace TicTacToe;
+
+/// <summary>
+/// Global game state stored on the singleton entity.
+/// </summary>
+[MessagePackObject]
+public struct GameState
+{
+    [Key(0)] public Player CurrentPlayer;
+    [Key(1)] public GameStatus Status;
+    [Key(2)] public int MoveCount;
+}

TicTacToe/Singletons/GameStatus.cs

@@ -0,0 +1,9 @@
+namespace TicTacToe;
+
+public enum GameStatus : byte
+{
+    Playing = 0,
+    XWon = 1,
+    OWon = 2,
+    Draw = 3
+}