feat v1.33.0: background editor — visual decor layer

- third mode tab: draw lines/rects/ovals/text with grid snap, drag
  preview; select+move (Delete key), erase, color/width/fill controls;
  Esc ladder; text dialog with S/M/L sizes and dblclick re-edit
- decor renders under rooms, visible in every mode, click-transparent
  outside its editor; stored in space.decor with backend schema
  (line/rect/ellipse/text variants), rev/optimistic locking as usual
- smoke_decor.mjs (19 checks); smoke_editor_tabs updated to 3 tabs;
  TESTING/CHANGELOG/UX-MODES same-commit

docs/CHANGELOG.md

@@ -1,5 +1,18 @@
 # Changelog
 
+## v1.33.0 — 2026-07-22 (background editor)
+- New third mode: **Background editor**. Draw purely visual decor on the plan —
+  lines, rectangles, ovals and text labels that never interact with rooms,
+  devices or fills. Shapes are drag-drawn with grid snap and a live preview;
+  text is placed via a small dialog (size S/M/L, color; double-click to edit).
+  Toolbar: Select (move, Delete key), Erase, color, three line widths and an
+  optional 25% fill for rects/ovals. Esc walks back: draft → selection →
+  Select tool → View.
+- The decor layer renders **under rooms** (a true underlay), is visible in all
+  modes and completely click-transparent outside the editor. Stored per space
+  in the server config (`space.decor`, validated on the backend, shared across
+  clients with the usual rev/optimistic locking).
+
 ## v1.32.1 — 2026-07-22
 - Opening tool: hovering near a wall now shows a **dashed preview** of where
   the opening would land — snapped onto the wall, default door length (90 cm),

docs/TESTING.md

@@ -140,6 +140,13 @@ Run the *core flows* (marked ★ below) in each environment at least once per mi
       (explicit ripple color still wins); off/white lights unchanged [auto]
 - [ ] Alarm pulse (v1.27.0): leak/smoke/gas/CO/siren in 'on' pulse a red ring over any
       display mode; clears on 'off'; unavailable never alarms [auto]; reduced-motion static
+- [ ] Background editor (v1.33.0): third tab with its own toolbar (select /
+      line / rect / oval / text / erase + color, width, fill, X); shapes drag-
+      drawn with grid snap and live preview; degenerate shapes dropped; text
+      via dialog (S/M/L, color; dblclick re-edits); Select moves (snap), Delete
+      removes, Erase deletes on click; Esc: draft → selection → select tool →
+      View; decor renders under rooms, visible everywhere, inert outside the
+      editor; stored in space.decor (rev/lock, backend schema) [auto]
 - [ ] Opening hover preview (v1.32.1): with the Opening tool, hovering near a
       wall shows a dashed 90 cm ghost snapped onto the wall (with a center
       dot); no ghost far from walls, over an existing opening (click = edit),

docs/UX-MODES.md

@@ -12,7 +12,10 @@ A segmented control in the card header with three tabs; the active one is visual
 highlighted, and edit modes add a colored frame around the stage so the mode is
 obvious at a glance:
 
-**[ 📐 Plan editor ] [ 🔧 Device editor ]** — View has NO tab (since v1.30.2).
+**[ 📐 Plan editor ] [ 🔧 Device editor ] [ ✏️ Background editor ]** — View has
+NO tab (since v1.30.2). The Background editor (v1.33.0) manages a purely visual
+decor layer (lines/rects/ovals/text in `space.decor`, drawn under the rooms,
+inert everywhere outside its editor).
 
 - **View** is the implicit default state: no editor tab is active. It is the only
   state after every load (edit modes are never restored across reloads).