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/i18n/en.json

@@ -128,8 +128,8 @@
   "toast.room_overlap": "The outline overlaps room “{name}” — rooms must not overlap",
   "toast.merge_not_adjacent": "Only rooms that share a wall can be merged",
   "toast.rooms_merged": "Rooms merged into “{name}”",
-  "toast.split_pick_wall": "Click a grid dot on the room’s wall",
-  "toast.split_bad_cut": "The cut must be a straight line from wall to wall, inside the room",
+  "toast.split_pick_wall": "Start the cut on the room’s wall",
+  "toast.split_bad_cut": "The cut must run wall to wall inside the room, without crossing walls or itself",
   "merge.header": "Merge rooms",
   "merge.hint": "The merged room keeps one name and one area. The other area is released — its devices leave the plan until another room claims it.",
   "merge.keep": "Keep",
@@ -260,5 +260,6 @@
   "space.label_light": "Lights on/off",
   "roomcard.light_on": "On",
   "roomcard.light_off": "Off",
-  "roomcard.light_partial": "{on} of {total}"
+  "roomcard.light_partial": "{on} of {total}",
+  "toast.split_pick_inside": "Intermediate cut points must be inside the room"
 }