Add Overview UI icon set, Icon Button prefab and hover/disabled ring

- 7 generated icons (settings, statistics, paint, freecam, thirdperson,
  firstperson v3 viewfinder, spectator eye) + hand-painted hover ring,
  full-res PNGs imported as sprites (max size 256)
- Icon Background texture (user asset)
- IconButtonHover: shows the Hover child on pointer hover or while the
  button is non-interactable (doubles as active-mode marker)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Assets/Scripts/Components/UI/IconButtonHover.cs

@@ -0,0 +1,51 @@
+using UnityEngine;
+using UnityEngine.EventSystems;
+using UnityEngine.UI;
+
+/// <summary>
+/// Shows the hover overlay child of an icon button while the pointer is over
+/// the button or while the button is not interactable (marks the active mode).
+/// </summary>
+public class IconButtonHover : MonoBehaviour, IPointerEnterHandler, IPointerExitHandler
+{
+    [SerializeField, Tooltip("Overlay object toggled on hover / while the button is disabled.")]
+    private GameObject hover;
+
+    [SerializeField, Tooltip("Button whose interactable state drives the disabled case. Defaults to the Button on this object.")]
+    private Button button;
+
+    private bool _pointerInside;
+
+    private void Awake()
+    {
+        if (!button) button = GetComponent<Button>();
+    }
+
+    private void OnDisable()
+    {
+        _pointerInside = false;
+        Refresh();
+    }
+
+    public void OnPointerEnter(PointerEventData eventData)
+    {
+        _pointerInside = true;
+        Refresh();
+    }
+
+    public void OnPointerExit(PointerEventData eventData)
+    {
+        _pointerInside = false;
+        Refresh();
+    }
+
+    // Poll each frame: Button has no event for interactable changes (OverviewMenu
+    // flips it on refresh), and this only runs on a handful of menu buttons.
+    private void LateUpdate() => Refresh();
+
+    private void Refresh()
+    {
+        bool want = _pointerInside || (button && !button.interactable);
+        if (hover && hover.activeSelf != want) hover.SetActive(want);
+    }
+}