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/InputUtil.cs

@@ -104,4 +104,21 @@ public static class InputUtil
         return Input.GetMouseButtonDown(0);
 #endif
     }
+
+    /// <summary>Gameplay key pressed on this exact frame (edge), suppressed while a UI text field is
+    /// focused so typing never triggers gameplay bindings. The parameter type follows the active input
+    /// backend, matching how the callers' serialized key fields are declared.</summary>
+#if ENABLE_INPUT_SYSTEM
+    public static bool GameplayKeyPressed(Key key)
+    {
+        if (TypingGuard.IsTyping) return false;
+        return Keyboard.current != null && Keyboard.current[key].wasPressedThisFrame;
+    }
+#else
+    public static bool GameplayKeyPressed(KeyCode key)
+    {
+        if (TypingGuard.IsTyping) return false;
+        return Input.GetKeyDown(key);
+    }
+#endif
 }