Mini Guide
Arrow Keys (↑ ↓ ← →): Move between cells with the keyboard.
Note Mode (N): Write candidate numbers or letters as small notes in the selected cell.
Hint (H): Fills the selected empty cell with the correct number or letter.
Clear (0/Del): Clears value, letter, or notes from the selected cell.
Undo (Backspace): Reverts your latest moves step by step.
