Added game over/restart UI and player behaviours.

main.gd

@@ -1,12 +1,14 @@
 extends Node2D
 
 @onready var start_button = $CanvasLayer/CenterContainer/Start
+@onready var game_over = $CanvasLayer/CenterContainer/GameOver
 
 var enemy = preload("res://enemy.tscn")
 var score = 0
 
 func _ready():
     start_button.show()
+    game_over.hide()
 #   spawn_enemies()
 
 func new_game():
@@ -28,6 +30,12 @@ func _on_enemy_died(value):
     score += value
     $CanvasLayer/UI.update_score(score)
 
+func _on_player_died():
+    get_tree().call_group("enemies", "queue_free")
+    game_over.show()
+    await get_tree().create_timer(2).timeout
+    game_over.hide()
+    start_button.show()
 
 func _on_start_pressed():
     start_button.hide()