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

scripts/level_0.gd

@@ -0,0 +1,13 @@
+extends Node2D
+
+@onready var player = $player
+@onready var hud = $HUD
+
+func _ready():
+	if player:
+		player.health_changed.connect(hud.update_health)
+		player.died.connect(hud.show_game_over)
+		
+		var turret = player.get_node("turret")
+		if turret:
+			turret.ammo_changed.connect(hud.update_ammo)