Add split-screen Space Shooter with pod steering and boost.

Two-player mode with client assignment, 3D vector calibration for cylindrical
pods, lives, tap/double-tap boost with low-intensity LED cooldown feedback,
and Kenney sprite assets.

Co-authored-by: Cursor <cursoragent@cursor.com>

scripts/sprite_atlas.gd

@@ -0,0 +1,40 @@
+class_name SpriteAtlas
+extends RefCounted
+
+static var _sheet: Texture2D
+
+
+static func sheet() -> Texture2D:
+	if _sheet == null:
+		_sheet = load("res://assets/Spritesheet/sheet.png")
+	return _sheet
+
+
+static func region(x: int, y: int, w: int, h: int) -> AtlasTexture:
+	var tex := AtlasTexture.new()
+	tex.atlas = sheet()
+	tex.region = Rect2i(x, y, w, h)
+	return tex
+
+
+static func named(name: String) -> AtlasTexture:
+	match name:
+		"meteorBrown_big1":
+			return region(224, 664, 101, 84)
+		"playerShip1_blue":
+			return region(211, 941, 99, 75)
+		"playerShip1_orange":
+			return region(247, 84, 99, 75)
+		"laserBlue01":
+			return region(856, 421, 9, 54)
+		"laserRed01":
+			return region(858, 230, 9, 54)
+		"laserGreen01":
+			return region(855, 173, 9, 57)
+		"star1":
+			return region(628, 681, 25, 24)
+		"star2":
+			return region(222, 84, 25, 24)
+		_:
+			push_warning("SpriteAtlas: unknown sprite '%s'" % name)
+			return region(0, 0, 1, 1)