Audio: per-SoundEffect occlusion via Steam Audio + 3D flag refactor

- New occlusion opt-in on SoundEffect: spatialized instances get a
  SteamAudioSource with raycast occlusion + frequency-dependent
  transmission (walls muffle instead of hard-mute)
- Replace SoundEffectDistanceRange asset indirection with an explicit
  _3d bool (user refactor); rolloff/distance now left to defaults
- Hey.asset: occlusion enabled

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

Assets/Scripts/Audio/SoundEffect.cs

@@ -7,7 +7,6 @@ namespace Prototype
     [CreateAssetMenu(menuName = "Prototype/Sound Effect")]
     public class SoundEffect : ScriptableObject
     {
-        [SerializeField] SoundEffectDistanceRange distanceRange;
         [SerializeField] Vector2 volumeMultiplier = new(1, 1);
         [SerializeField] Vector2 pitch = new(.95f, 1.05f);
 
@@ -15,7 +14,10 @@ namespace Prototype
         public AudioMixerGroup audioMixerGroup;
         public float volumeMultiplierFactor = 1;
         [SerializeField] bool loop;
+        [SerializeField] bool _3d;
         [SerializeField] bool spatialize;
+        [Tooltip("Occlude/muffle the sound behind walls via Steam Audio. Requires spatialize and exported scene geometry.")]
+        [SerializeField] bool occlusion;
 
         [Header("Additional Settings")]
         [SerializeField, Range(0, 1)] float defaultVolume = .8f;
@@ -35,8 +37,9 @@ namespace Prototype
             volumeMultiplier = Random.Range(volumeMultiplier.x, volumeMultiplier.y) * volumeMultiplierFactor,
             pitch = Random.Range(pitch.x, pitch.y),
             loop = loop,
+            _3d = _3d,
             spatialize = spatialize,
-            distanceRange = distanceRange ? distanceRange.range : null
+            occlusion = occlusion
         };
 
 #if UNITY_EDITOR