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.

src/logic.ts

@@ -97,7 +97,13 @@ export function snapToWall(
     const d = Math.hypot(p[0] - q[0], p[1] - q[1]);
     if (d < bestD) {
       bestD = d;
-      best = { x: q[0], y: q[1], angle: (Math.atan2(dy, dx) * 180) / Math.PI };
+      // normalize to [-90, 90): two rooms sharing a wall yield the same edge in
+      // OPPOSITE directions — without this, dragging an opening across segment
+      // boundaries would flip its hinge side back and forth
+      let angle = (Math.atan2(dy, dx) * 180) / Math.PI;
+      if (angle >= 90) angle -= 180;
+      else if (angle < -90) angle += 180;
+      best = { x: q[0], y: q[1], angle };
     }
   }
   return best;