feat v1.23.1: openings — hover outline, drag along walls, double-click properties

- Hover: an accent outline hugs the opening's wall strip + grab cursor.
- Drag (view mode): re-snaps continuously to the nearest derived wall; snapToWall now
  normalizes the angle to [-90,90) — neighbouring rooms yield the same wall in opposite
  directions, which used to flip the hinge while dragging across segment boundaries.
  setPointerCapture wrapped in try/catch (an inactive pointerId must not kill the drag).
- Click still opens the status card (via a 250ms timer); double click opens the
  properties dialog from view mode. Hit zone is now a slightly thicker strip along the
  wall instead of the whole swing square (fewer accidental hovers). +1 test (77).
Verified live: drag moved a test door exactly along a vertical wall (angle 90 -> -90),
click/dblclick/markup-tool paths all работают; the user's 12 real openings untouched.

docs/TESTING.md

@@ -223,3 +223,9 @@ require hands on real hardware — they remain for the human pass.
       the lock can NOT be toggled from the plan
 - [ ] Flip toggles mirror the hinge side and the swing side
 - [ ] Click an existing opening with the tool → edit dialog; Delete removes it
+- [ ] (v1.23.1) Hovering an opening in view mode shows the accent outline + grab cursor
+- [ ] Dragging an opening slides it along walls (re-snapping, incl. around corners) and saves
+      on release; dragging far away from walls leaves it in place; hinge does not flip while
+      crossing wall-segment boundaries
+- [ ] Single click still opens the status card; double click opens the properties dialog;
+      a drag does NOT open either