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

scenes/bullet_he.tscn

@@ -0,0 +1,21 @@
+[gd_scene load_steps=4 format=3 uid="uid://bullethe68aa0"]
+
+[ext_resource type="Script" path="res://scripts/bullet.gd" id="1_bullet"]
+[ext_resource type="Texture2D" uid="uid://ddmjl3yshqcjw" path="res://icon.svg" id="2_icon"]
+
+[sub_resource type="RectangleShape2D" id="RectangleShape2D_1"]
+size = Vector2(20, 20)
+
+[node name="BulletHE" type="Area2D"]
+script = ExtResource("1_bullet")
+speed = 400.0
+damage = 20.0
+ammo_type = 1
+
+[node name="Sprite2D" type="Sprite2D" parent="."]
+modulate = Color(1, 0, 0, 1)
+scale = Vector2(0.25, 0.25)
+texture = ExtResource("2_icon")
+
+[node name="CollisionShape2D" type="CollisionShape2D" parent="."]
+shape = SubResource("RectangleShape2D_1")