Refactor: extract shared helpers across scripts, trim remaining doc redundancy

Deduplication pass (44 extractions):
- New SmoothedLook: shared smoothed yaw/pitch look tick + view seeding
  (FirstPersonController, FreeCamController)
- New CharacterTeleport: disable-CC-around-teleport idiom (rescue,
  owner position apply, free-cam sync)
- New GeometryUtil: RescaleToUnitScale + TransformBounds (concealment
  meter/volume, skinned collider baker)
- Paint family: canonical map read/write shared between Net and
  Persistence, snapshot decode, backend stroke dispatch, RebuildBackend,
  ResolveSeed, chunked RPC send/gate/copy, CamoKnobs/HeightKnobs
  aggregates, SanitizeFileKey, NewMaskTexture, AdoptAlbedo, FindSlider
- Player/modes: GameMode SetPlayerControl/SetPainting/SetOrbitInputEnabled,
  InputUtil.GameplayKeyPressed, NearestClimbHit, ComputeXRay delegates to
  ComputeResolutionFreeze, FingerIK TryInPlaneAngle
- Match/misc: UnhookSessionCallbacks, SendEmptyNamedMessage, SwapScenes,
  RunSessionOpAsync, CovarianceEigen, CollectClusterPoints, MatchHud
  GUIStyle cache, HsvColorPicker rehook, VoxelCenter

Documentation pass: remove 6 triplicated doc blocks and 2 restating
inline comments left after the previous reduction.

Behavior-neutral; hot-path rasterizer loops intentionally untouched.

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

Assets/Scripts/FingerIK.cs

@@ -306,11 +306,8 @@ public class FingerIK : MonoBehaviour
 
                 // World hinge axis (invariant under the joint's own twist about local X).
                 Vector3 axisW = (j.rotation * HingeAxis(i)).normalized;
-                Vector3 tipPlane = Vector3.ProjectOnPlane(toTip, axisW);
-                Vector3 tgtPlane = Vector3.ProjectOnPlane(toTarget, axisW);
-                if (tipPlane.sqrMagnitude < 1e-10f || tgtPlane.sqrMagnitude < 1e-10f) continue;
+                if (!TryInPlaneAngle(toTip, toTarget, axisW, out float hingeAng)) continue;
 
-                float hingeAng = Vector3.SignedAngle(tipPlane, tgtPlane, axisW);
                 j.rotation = Quaternion.AngleAxis(hingeAng, axisW) * j.rotation;
 
                 ConstrainToHinge(i);
@@ -367,16 +364,25 @@ public class FingerIK : MonoBehaviour
         Vector3 toTip = tip.position - b.position;
         Vector3 toTarget = target.position - b.position;
 
-        float latAng = 0f;
-        Vector3 tipPlane = Vector3.ProjectOnPlane(toTip, axisW);
-        Vector3 tgtPlane = Vector3.ProjectOnPlane(toTarget, axisW);
-        if (tipPlane.sqrMagnitude > 1e-10f && tgtPlane.sqrMagnitude > 1e-10f)
-            latAng = Vector3.SignedAngle(tipPlane, tgtPlane, axisW);
+        TryInPlaneAngle(toTip, toTarget, axisW, out float latAng); // degenerate -> 0 (spread bias still applies)
 
         latAng = Mathf.Clamp(latAng + spread, spreadLimits.x, spreadLimits.y);
         _solvedLocal[0] = _solvedLocal[0] * Quaternion.AngleAxis(latAng, SpreadAxis);
     }
 
+    // Signed angle from toTip to toTarget projected onto the plane orthogonal to axis; false when
+    // either projection is degenerate (angle is then 0 and must not be applied as a solve step).
+    private static bool TryInPlaneAngle(Vector3 toTip, Vector3 toTarget, Vector3 axis, out float angle)
+    {
+        angle = 0f;
+        Vector3 tipPlane = Vector3.ProjectOnPlane(toTip, axis);
+        Vector3 tgtPlane = Vector3.ProjectOnPlane(toTarget, axis);
+        if (tipPlane.sqrMagnitude < 1e-10f || tgtPlane.sqrMagnitude < 1e-10f) return false;
+
+        angle = Vector3.SignedAngle(tipPlane, tgtPlane, axis);
+        return true;
+    }
+
     // Base-joint spread/opposition about local Z, composed AFTER curl so the two DOFs don't
     // fight. Applied on the final base rotation when IK isn't driving the base laterally.
     private void ApplySpread()