feat v1.32.0: polyline split, tool cursors, Esc walk-back in merge/split

- splitRoomPath in logic.ts: wall-to-wall polyline cut with interior
  vertices; validates wall crossings, self-intersection, degenerate
  parts; splitRoom delegates (2-point path); +3 unit tests (93 total)
- split UI: interior clicks add snapped intermediate points, live
  polyline + vertices + preview; new/updated toasts
- cursors: pointer for merge/delroom and split room-pick stage,
  crosshair while cutting (stage tool-* classes)
- Esc: split — drop last point, then room pick, then back to draw;
  merge — clear selection, then back to draw
- smoke_split_polyline.mjs (14 checks); TESTING/CHANGELOG same-commit

src/styles.ts

@@ -445,6 +445,12 @@ export const cardStyles = css`
     .stage.markup {
       cursor: crosshair;
     }
+    /* room-picking stages: merge (both clicks) and split before a room is chosen */
+    .stage.markup.tool-merge,
+    .stage.markup.tool-split.pickstage,
+    .stage.markup.tool-delroom {
+      cursor: pointer;
+    }
     .stage.markup .room {
       pointer-events: none;
     }