Feature: per-tower construction-phase build bisuals

Adding the correct pipeline for creating the different building phases for towers. Adding a default set with primitive cubes.

Assets/_Project/Scripts/Towers/ConstructionPhaseSet.cs

@@ -0,0 +1,32 @@
+// Assets/_Project/Scripts/Towers/ConstructionPhaseSet.cs
+using UnityEngine;
+
+namespace TD.Towers
+{
+    /// <summary>
+    /// An ordered set of construction-stage visuals a build site transitions between as a
+    /// tower is built — typically 3 assets (early → mid → late). A tower references its own
+    /// set via <see cref="TowerDefinition.ConstructionPhases"/>; build sites fall back to a
+    /// project-default set when a tower doesn't define one.
+    /// </summary>
+    /// <remarks>
+    /// The entries are <b>shape</b> prefabs only. <c>BuildSiteVisual</c> applies the
+    /// queued (green) / constructing / paused materials and the owner tint on top, so the
+    /// phase assets don't need their own build-state materials. Keep them simple
+    /// (single material) — the build site swaps the active phase's renderer material.
+    /// </remarks>
+    [CreateAssetMenu(fileName = "ConstructionPhaseSet", menuName = "TD/Construction Phase Set")]
+    public class ConstructionPhaseSet : ScriptableObject
+    {
+        [Tooltip("Ordered construction-stage prefabs. Shown in sequence as the build " +
+                 "progresses — e.g. 3 entries = early / mid / late thirds of the build.")]
+        [SerializeField] private GameObject[] phases;
+
+        /// <summary>Number of construction phases in this set.</summary>
+        public int PhaseCount => phases != null ? phases.Length : 0;
+
+        /// <summary>The phase prefab at <paramref name="index"/>, or null if out of range.</summary>
+        public GameObject GetPhase(int index)
+            => (phases != null && index >= 0 && index < phases.Length) ? phases[index] : null;
+    }
+}

Assets/_Project/Scripts/Towers/ConstructionPhaseSet.cs.meta

@@ -0,0 +1,11 @@
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Assets/_Project/Scripts/Towers/TowerDefinition.cs

@@ -68,6 +68,11 @@ namespace TD.Towers
                  "replace with a real mesh when art is available.")]
         public GameObject TowerPrefab;
 
+        [Tooltip("Optional per-tower construction-stage visuals shown while this tower is " +
+                 "being built. Leave empty to use the project-default set assigned on the " +
+                 "BuildSiteVisual prefab.")]
+        public ConstructionPhaseSet ConstructionPhases;
+
         [Tooltip("Icon shown on this tower's tile in the HUD build menu. Auto-generated from " +
                  "the TowerPrefab by the 'TD/Generate Tower Icons' menu item, or assign a " +
                  "Sprite manually. Null falls back to the grey placeholder icon.")]