Scene split: MainMenu frontend + Game gameplay scenes; build/render settings

Add MainMenu.unity (build index 0, UITK frontend) alongside Game.unity (index 1); reorder EditorBuildSettings; URP/volume profile + project settings updates supporting the menu/game split.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Assets/Settings/DefaultVolumeProfile.asset

@@ -342,6 +342,9 @@ MonoBehaviour:
   skyOcclusionIntensityMultiplier:
     m_OverrideState: 1
     m_Value: 1
+  worldOffset:
+    m_OverrideState: 1
+    m_Value: {x: 0, y: 0, z: 0}
 --- !u!114 &-1216621516061285780
 MonoBehaviour:
   m_ObjectHideFlags: 3
@@ -376,6 +379,9 @@ MonoBehaviour:
   highQualityFiltering:
     m_OverrideState: 1
     m_Value: 0
+  filter:
+    m_OverrideState: 1
+    m_Value: 0
   downscale:
     m_OverrideState: 1
     m_Value: 0
@@ -462,8 +468,6 @@ MonoBehaviour:
   - {fileID: -6288072647309666549}
   - {fileID: 7518938298396184218}
   - {fileID: -1410297666881709256}
-  - {fileID: -7750755424749557576}
-  - {fileID: -5139089513906902183}
 --- !u!114 &853819529557874667
 MonoBehaviour:
   m_ObjectHideFlags: 3