feat: Game scene — SongController bridges custom map to VRBeatsKit

- SongController: loads MP3 + Beat Saber JSON map, runs countdown (3→2→1→GO),
  spawns cubes via VR_BeatManager.Spawn() synced to audioSource.time
- NoteData → SpawnEventInfo mapping: position/lineLayer → x/y, colorType → ColorSide,
  cutDirection → Direction enum
- travelTimeOverride on SpawnEventInfo: each cube's travel time is back-calculated
  from remaining time at spawn moment, so simultaneous notes arrive at hit zone together
  regardless of frame-level spawn delay
- AudioManager: add PlayClip(AudioClip) and CurrentTime property
- VR_BeatManager: respect travelTimeOverride when non-zero
- Settings.asset: targetTravelTime 0.5 → 1.8 for natural Beat Saber approach feel
- SceneBuilder ④: auto-builds Game.unity from SaberStyle, wires SongController refs,
  registers in Build Settings
- LiberationSans SDF fallback updated with NanumGothic for Korean text support
- Remove unused SampleScene

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

ProjectSettings/EditorBuildSettings.asset

@@ -17,6 +17,9 @@ EditorBuildSettings:
   - enabled: 1
     path: Assets/VRBeatsKit/Scenes/SaberStyle.unity
     guid: bb4ee84e66cce254e9cbf1fdfc136c08
+  - enabled: 1
+    path: Assets/Scenes/Game.unity
+    guid: dab0572fcafe87d4b80a838fd874234b
   m_configObjects:
     Unity.XR.Oculus.Settings: {fileID: 11400000, guid: c872ebb38c96a954ca6549564e1aa398,
       type: 2}