Fire control Cut 6b: a shot's dice belong to the shot, and airburst resolves in the simulation

6.1 (Soul finding 6): Commit builds a local CultMath.Random from (Zone.CombatSeed,
shot.ShotId) instead of reading and writing the shared ItemManager.Random stream.
Zone exposes CombatSeed (the same expression that already seeds its own _random),
so a shot's outcome is a pure function of zone identity and shot id -- immune to
whatever else drew from the shared stream in between.

6.2 (Soul finding 5): airburst is wired into the simulation instead of back into
Projectile.cs. PendingShot gains BurstPosition/BurstRadius, frozen at Fire time
from PredictedIntercept and the weapon's authored WeaponItemData.AirburstRange
when WeaponModifiers carries Airburst. FireControl.Step resolves such a shot via
Splash instead of Apply, never both. Projectile.cs/ProjectileManager.cs drop the
dead AirburstDistance/AirburstRange fields and write-back.

Tests: FireControlCut6Tests.cs pins both rules (208 baseline + 5 new, all green).

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

Assets/Scripts/ServerShared/ItemData.cs

@@ -489,6 +489,13 @@ public class WeaponItemData : GearData
     
     [Inspectable, JsonProperty("modifiers"), Key(28)]
     public WeaponModifiers WeaponModifiers;
+
+    // Cut 6b (docs/fire-control-cut.md, 6.2): the authored blast radius an Airburst-flagged weapon's shot
+    // splashes with at arrival, frozen into PendingShot.BurstRadius at fire. Zero (and unread) for a weapon
+    // without the Airburst flag. No authored value exists yet -- the flag is wired and unexercised until Cut
+    // 6a or a later authoring pass sets it.
+    [Inspectable, JsonProperty("airburstRange"), Key(29)]
+    public float AirburstRange;
 }
 
 [CultDocument("aetheria.hulldata", "1"), Inspectable, MessagePackObject, JsonObject(MemberSerialization.OptIn)]