Gravity grid-lowering: the drawn height is one Gravity Field pass over the zone's wells; gravity brushes and brush inputs deleted

Zone.WellReference owns each body's reference zero (GetHeight uses it). Gravity.cginc mirrors GravityField.Potential;
Brushes/Gravity Field draws depth = -h on layer 9 from a StructuredBuffer that GravityLowering.Lower fills from the
zone each frame; GravityLowering.CreateField makes the one quad. GravityFieldParityVerify renders it and compares every
texel with -Zone.GetHeight (max error 0.0059 u), the gradient with GetForce (0.03 degrees) and the wiring.

Deleted: the Gravity Well children of Planet, Gas Giant, Sun and PlanetOutpost prefabs, Wormhole 1's three gravity
children, their overrides in Main Menu and TestScene, five wormhole/wave materials and two brush shaders,
Planet.GravityWellDepth/Radius, BodyData keys 6-7, PlanetSettings.GravityDepth/GravityRadius (and the Settings.asset
keys). Surface Displacement culls layer 9 only. Headless build and tests not yet run at this commit.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Assets/Scripts/ServerShared/ZoneData.cs

@@ -86,12 +86,6 @@ public abstract class BodyData
 
     [JsonProperty("bodyRadiusMul")] [Key(5)]
     public float BodyRadiusMultiplier = 1;
-
-    [JsonProperty("gravRadiusMul")] [Key(6)]
-    public float GravityRadiusMultiplier = 1;
-
-    [JsonProperty("depthMul")] [Key(7)]
-    public float GravityDepthMultiplier = 1;
 }
 
 [CultDocument("aetheria.planetdata", "1"), MessagePackObject, JsonObject(MemberSerialization.OptIn)]