Adding the feature to sell towers with VFX and audio included

Assets/_Project/Scripts/VFX/TransientEffect.cs

@@ -0,0 +1,30 @@
+// Assets/_Project/Scripts/VFX/TransientEffect.cs
+using UnityEngine;
+
+namespace TD.VFX
+{
+    /// <summary>
+    /// Destroys its GameObject a fixed time after it spawns. Drop this onto any one-shot
+    /// effect prefab — a particle burst, a VFX Graph effect, a sound-only object — so it
+    /// cleans itself up without any bespoke code. Designed for prefabs spawned by
+    /// <see cref="SellEffectSpawner"/> (and any future effect spawner) that fire once and
+    /// should disappear.
+    /// </summary>
+    /// <remarks>
+    /// <b>Shuriken shortcut:</b> a plain <see cref="ParticleSystem"/> can instead self-destroy
+    /// with no component at all — set <i>Main → Stop Action → Destroy</i> and make sure Looping
+    /// is off. Use this component for <b>VFX Graph</b> effects (which have no Stop Action) or for
+    /// prefabs that combine several systems and need one predictable lifetime.
+    ///
+    /// <para>Set <see cref="lifetime"/> to comfortably exceed the effect's visible duration so it
+    /// isn't cut off mid-play.</para>
+    /// </remarks>
+    public class TransientEffect : MonoBehaviour
+    {
+        [Tooltip("Seconds after spawn before this GameObject destroys itself. Set it a little " +
+                 "longer than the effect's visible length so nothing is cut off.")]
+        [SerializeField, Min(0f)] private float lifetime = 1.5f;
+
+        private void Start() => Destroy(gameObject, lifetime);
+    }
+}