Feature Request: Add Multi-Level Undo Functionality

The current game (if undo exists) typically allows only a single undo, limiting flexibility for players who accidentally make multiple misclicks. This restriction can frustrate both casual and strategic players who wish to experiment with different move sequences.

🎯 Proposed Solution

• Extend undo capability to store and revert the last 3–5 moves.
• Maintain a stack of previous game states (board, score, move count).
• Implement keyboard shortcut (e.g., Ctrl + Z) or on-screen Undo button.
• Limit undo count per game (configurable setting to avoid abuse).

✅ Expected Behavior

• Players can revert multiple consecutive moves.
• Undo is smooth, instantaneous, and doesn’t affect game performance.
• Undo history resets when a new game starts.

💻 Technical Notes

• Use a stack data structure to store snapshots of game states.
• Each state includes: tile positions, score, and move history.
• Manage memory efficiently — discard old states beyond the limit.

🧪 Test Steps

1. Play a game and make several moves.
2. Press Undo repeatedly → verify previous states restore correctly.
3. Ensure score and animations revert as expected.
4. Start a new game → undo history clears.