Cut 6d: the dart-throw kernel replaces the coin-flip landing rule

FireControl.Commit used to place a hit with a coin flip between exactly
the aimed item and a uniform-random hull cell -- no spatial term, so a
near-miss on a stern item was as likely to land in the bow as the stern.

One Gaussian kernel, in hull-schematic cell units, now decides both
halves of "where will this shot go": w(cell) = exp(-d^2/2*sigma^2) over
every occupied cell, sigma = 1/Precision. HitProbability folds the
kernel's on-hull mass share (pOnHull) into PBase at fire time (R10/Q6
unaffected); Commit draws the landing cell from the same weights. A shot
that passes the roll always lands on metal -- the off-hull chance is
priced into that one roll, never resolved as a second miss stage. The
uniform-random branch is deleted outright, not demoted.

Precision now feeds every shot's pOnHull, aimed or not, so its unaided
fallback (FireControl.Precision) reads GameplaySettings.UnaidedPrecision
instead of a bare 0 -- the same shape as the existing UnaidedAccuracy/
UnaidedTracking floors. pOnHull is saturated: the discrete sum over-
estimates the continuous kernel's integral once sigma drops below about
one cell, and a mass share cannot exceed the whole kernel.

Existing fixtures across FireAuthorityTests, FireControlCut4/5/6Tests and
TargetingSystemTests authored Precision as 0 (or relied on the old 0
fallback) purely as a don't-care value under the coin-flip rule, where it
only gated the aimed-item branch. Under the kernel it drives every shot's
sigma, so those fixtures are re-authored to keep pOnHull near its
ceiling and stay pinned on what they actually test.

mutation_tests_fire_control_cut3.sh's two anchors into HitProbability's
return line and the deleted coin-flip branch are updated to the
equivalent lines/mutations on the new code.

Assets/Scripts/ServerShared/Behaviors/TargetingSystem.cs

@@ -29,8 +29,11 @@ public class TargetingSystemData : BehaviorData
     [Inspectable, JsonProperty("resolution"), Key(2), RuntimeInspectable]
     public PerformanceStat Resolution = new PerformanceStat();
 
-    // The chance a hit lands on the item actually aimed at (Entity.TargetItem) rather than a random cell.
-    // Consumed by Cut 3's roll.
+    // Cut 6d (docs/fire-control-cut.md): grouping tightness, not a probability. FireControl.Sigma derives a
+    // Gaussian kernel's sigma as 1/Precision, in hull-schematic cell units -- a higher number groups tighter
+    // around whatever is aimed at (Entity.TargetItem's cells, or the hull's own centre of mass unaimed).
+    // Consumed by Cut 3's roll (folded into HitProbability as pOnHull) and by Commit's cell draw, both through
+    // the one kernel function -- never re-derived separately.
     [Inspectable, JsonProperty("precision"), Key(3), RuntimeInspectable]
     public PerformanceStat Precision = new PerformanceStat();