ux v1.32.1: dashed hover preview for the Opening tool

- _openingPreview getter mirrors the click's snap (same eps, same
  existing-opening hit test); dashed 90cm ghost + center dot on the wall
- smoke_opening_preview.mjs; TESTING/CHANGELOG same-commit

src/styles.ts

@@ -432,6 +432,19 @@ export const cardStyles = css`
       user-select: none;
       z-index: 3;
     }
+    .opghost {
+      stroke: var(--hp-open, #ff9800);
+      stroke-width: 5;
+      stroke-linecap: round;
+      stroke-dasharray: 7 6;
+      opacity: 0.85;
+      pointer-events: none;
+    }
+    .opghost-dot {
+      fill: var(--hp-open, #ff9800);
+      opacity: 0.85;
+      pointer-events: none;
+    }
     .rlabel {
       fill: var(--hp-muted);
       font-size: 15px;