M3.41: Stroke panel follows Units > Stroke, shows mixed values blank and reaches the Control bar

- Weights and dash lengths show in Units > Stroke in the Stroke panel,
  the Control bar and the Properties panel (Session::stroke_unit).
- Values the selected objects don't share show blank (weight, miter
  limit, dashes) or light no button (cap, join, align), from a
  per-revision cached DocState::stroke_mixed.
- Align Stroke Inside/Outside are disabled for open paths and type.
- The Control bar weight is a preset spinner with a width profile
  dropdown, and its Stroke link (and the Properties panel's) opens the
  Stroke panel as an anchored popover instead of docking it.
- The panels show a group's first painted object's stroke, as the
  Stroke proxy does (Session::shown_stroke).
- stroke.set on a group skips images and symbol instances.
- document.inspect reports each object's strokeOptions (cap, join,
  miterLimit, align, dash, dashOffset, alignDashes, arrows, arrowAlign,
  profile) in stroke.set terms.

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

crates/engine/src/lib.rs

@@ -801,6 +801,8 @@ mod tests_prefs;
 #[cfg(test)]
 mod tests_strokegeom;
 #[cfg(test)]
+mod tests_strokeux;
+#[cfg(test)]
 mod tests_styles;
 #[cfg(test)]
 mod tests_swatchcmds;