feat: Implement core game mechanics including player, enemies, bullets, HUD, and level setup.

scripts/hud.gd

@@ -0,0 +1,22 @@
+extends CanvasLayer
+
+@onready var health_bar = $Control/HealthBar
+@onready var game_over_screen = $GameOverScreen
+@onready var ap_label = $Control/AmmoContainer/APLabel
+@onready var he_label = $Control/AmmoContainer/HELabel
+
+func update_health(current, max_val):
+	health_bar.max_value = max_val
+	health_bar.value = current
+
+func update_ammo(ap, he):
+	ap_label.text = "AP: " + str(ap)
+	he_label.text = "HE: " + str(he)
+
+func show_game_over():
+	game_over_screen.show()
+	get_tree().paused = true
+
+func _on_restart_button_pressed():
+	get_tree().paused = false
+	get_tree().reload_current_scene()