feat: SongSelect UI polish — marquee title, button states, font

- MarqueeText: scrolling title for long song names (RectMask2D clipped)
- SongDetailPanel: difficulty selected = green (img.color direct set)
- SongSelectManager: ALL/OWNED tab active state via img.color
- Card layout: DestroyImmediate + correct rebuild order to fix zero-size title bug
- NanumGothic SDF fallback configured on LiberationSans for Korean support

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Assets/Script/SongDetailPanel.cs

@@ -33,8 +33,8 @@ public class SongDetailPanel : MonoBehaviour
     [Header("씬 이름")]
     [SerializeField] private string gameSceneName = "Game";
 
-    private static readonly Color SelectedColor   = new Color(0.2f, 0.78f, 0.4f);
-    private static readonly Color DeselectedColor = Color.white;
+    private static readonly Color SelectedColor     = new Color(0.2f, 0.78f, 0.4f);
+    private static readonly Color DeselectedImgColor = new Color(1f, 1f, 1f, 0.12f); // original button alpha
 
     private SongInfo          currentSong;
     private string            selectedDifficulty;
@@ -122,10 +122,17 @@ public class SongDetailPanel : MonoBehaviour
     {
         foreach (var (key, getBtn) in diffSlots)
         {
-            Button btn    = getBtn(this);
-            var    colors = btn.colors;
-            colors.normalColor = (key == selectedDifficulty) ? SelectedColor : DeselectedColor;
-            btn.colors = colors;
+            Button btn      = getBtn(this);
+            bool   selected = key == selectedDifficulty;
+
+            if (btn.targetGraphic is Image img)
+                img.color = selected ? SelectedColor : DeselectedImgColor;
+
+            var cb = btn.colors;
+            cb.normalColor      = Color.white;
+            cb.highlightedColor = selected ? new Color(0.3f, 0.95f, 0.55f) : new Color(1f, 1f, 1f, 0.25f);
+            cb.pressedColor     = selected ? new Color(0.15f, 0.6f, 0.3f)  : new Color(1f, 1f, 1f, 0.35f);
+            btn.colors          = cb;
         }
     }