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/SoundEffectOptions.cs

@@ -1,4 +1,3 @@
-using UnityEngine;
 using UnityEngine.Audio;
 
 namespace Prototype
@@ -17,8 +16,8 @@ namespace Prototype
         public bool? loop;
         public bool GetLoop() => loop ?? false;
 
-        public Vector2? distanceRange;
-        public Vector2 GetDistanceRange() => distanceRange ?? new(30, 200);
+        public bool? _3d;
+        public bool Get3D() => _3d ?? false;
 
         public bool? destroyOnLoad;
         public bool ShouldDestroyOnLoad() => destroyOnLoad ?? true;
@@ -28,5 +27,8 @@ namespace Prototype
 
         public bool? spatialize;
         public bool GetSpatialize() => spatialize ?? false;
+
+        public bool? occlusion;
+        public bool GetOcclusion() => occlusion ?? false;
     }
 }