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>

Assets/VRBeatsKit/Scripts/Core/AudioManager.cs

@@ -41,6 +41,14 @@ namespace VRBeats
             audioSource.outputAudioMixerGroup.audioMixer.SetFloat("Pitch", value);
         }
 
+        public void PlayClip(AudioClip clip)
+        {
+            audioSource.clip = clip;
+            audioSource.Play();
+        }
+
+        public float CurrentTime => audioSource != null ? audioSource.time : 0f;
+
     }
 
 }