docs: note tip-velocity physics is wired at capture

Co-authored-by: Cursor <cursoragent@cursor.com>

lib/editor/engine/pen_physics.dart

@@ -4,8 +4,7 @@
 // ink feels slightly thinner when moving fast (starvation), while ballpoint
 // stays nearly velocity-invariant.
 //
-// TODO(pen-physics-wire): wired at capture in PenCanvas._toNormalized via
-// tip velocity × pressure. PDF editor path still uses brush gamma only.
+// Wired at capture: PenCanvas._toNormalized and PenEditorScreen._pressureWithPhysics.
 
 import 'brush.dart';