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/styles.ts

@@ -233,10 +233,26 @@ export const cardStyles = css`
       stroke-width: 1.5;
       transition: stroke-dashoffset 0.6s ease;
     }
+    /* hover affordance: a rounded outline hugging the wall strip + a grab cursor */
+    .op-outline {
+      fill: none;
+      stroke: var(--hp-accent);
+      stroke-width: 1.5;
+      opacity: 0;
+      transition: opacity 0.15s;
+      pointer-events: none;
+    }
+    g.opening:hover .op-outline {
+      opacity: 0.9;
+    }
     .op-hit {
       fill: transparent;
-      cursor: pointer;
+      cursor: grab;
       pointer-events: auto;
+      touch-action: none; /* drags, not scrolls, on touch */
+    }
+    .op-hit:active {
+      cursor: grabbing;
     }
     .stage.markup .op-hit {
       pointer-events: none; /* markup clicks go to the stage tools */