Radar ping taunt sound + per-SoundEffect spatialize opt-in

MatchManager: new Radar Ping Sound property; MsgRadarPing now goes to
all clients (spawnBlips flag keeps blips hunter-only), sound plays 3D
at each pinged hider. Distance-based stagger (speed of sound + 35 ms
min gap) prevents phase cancellation when multiple hiders ping.

SoundEffect: new spatialize toggle (per asset, applied only to 3D
instances -> Steam Audio HRTF); removed unused fade field.

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

Assets/Scripts/Audio/SoundEffectInstance.cs

@@ -26,6 +26,7 @@ namespace Prototype
                 var range = options.GetDistanceRange();
 
                 audioSource.spatialBlend = range.x == 0 && range.y == 0 ? 0 : 1;
+                audioSource.spatialize = options.GetSpatialize() && audioSource.spatialBlend > 0;
                 audioSource.rolloffMode = AudioRolloffMode.Linear;
                 audioSource.minDistance = range.x;
                 audioSource.maxDistance = range.y;