feat(ultrasound): add UltrasoundMachine component with continuous heartbeat animation

scripts/objects/ultrasound_machine.gd

@@ -0,0 +1,23 @@
+## UltrasoundMachine — displays a continuous heartbeat pulse on the screen.
+class_name UltrasoundMachine extends Node2D
+
+const BEAT_RISE_DURATION: float = 0.12
+const BEAT_FALL_DURATION: float = 0.12
+const BEAT_INTERVAL: float = 0.60
+const BEAT_SCALE_PEAK: Vector2 = Vector2(1.5, 1.5)
+const BEAT_SCALE_REST: Vector2 = Vector2(1.0, 1.0)
+
+
+func _ready() -> void:
+	_start_heartbeat_loop()
+
+
+func _start_heartbeat_loop() -> void:
+	var dot: Node2D = get_node_or_null("HeartbeatDot") as Node2D
+	if dot == null:
+		return
+	var tween: Tween = create_tween()
+	tween.set_loops()
+	tween.tween_property(dot, "scale", BEAT_SCALE_PEAK, BEAT_RISE_DURATION)
+	tween.tween_property(dot, "scale", BEAT_SCALE_REST, BEAT_FALL_DURATION)
+	tween.tween_interval(BEAT_INTERVAL)