For this feature, I added a health system so the player has three
lives instead of losing instantly. In nav_game.py, I added "health": 3
to the game state, and in spaceship.py I created a take_damage method
that subtracts one life when the ship is hit. If the player's health
reaches zero, the game ends. This change is important because it
makes the game less punishing, gives the player more chances to
recover from mistakes, and makes gameplay feel more balanced and fun.
