feat v1.40.0: smart guides — alignment helper in every editor

- alignGuides/segmentAngle/is45 pure helpers (+2 unit tests, 108);
  per-context candidates (room vertices + path pts / other icons /
  decor endpoints+corners / other room cards), nearest per axis, max
  two guides, dashed accent lines with a source dot
- cursor badge shows length + angle, green on 45deg multiples
- indication only, no magnetism (owner's decision); guides live in
  plan/devices/decor, never in View
- smoke_align_guides.mjs (9 checks); TESTING/CHANGELOG same-commit

docs/CHANGELOG.md

@@ -1,5 +1,18 @@
 # Changelog
 
+## v1.40.0 — 2026-07-23 (smart guides)
+- **Alignment helper in every editor**: while drawing an outline, a cut or a
+  decor shape, and while dragging icons, room cards or decor, thin dashed
+  guides appear from the nearest object sharing your X and/or Y (one per
+  axis, with a marker dot at the source) — lamps line up, lines end exactly
+  above the end of a parallel line. Candidates follow the context: room
+  vertices and path points in the Plan editor, other icons in the Device
+  editor, decor endpoints/corners plus room vertices in the Background
+  editor, other room cards while dragging one.
+- The cursor badge now shows **length · angle** and turns green when the
+  segment's angle is a multiple of 45°. Guides are pure indication — the
+  grid keeps owning the actual position.
+
 ## v1.39.0 — 2026-07-23 (lights toggle by default)
 - Pure light sources — devices whose primary entity is a `light` (bulbs,
   chandeliers, night lights, light groups) — now **toggle on click by

docs/TESTING.md

@@ -140,6 +140,11 @@ 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
+- [ ] Smart guides (v1.40.0): while drawing (outline, cut, decor shapes) or
+      dragging (icons, room cards, decor) dashed accent guides appear from the
+      nearest object sharing the X and/or Y (max two, with a dot at the
+      source); the cursor badge shows length · angle and turns green on 45°
+      multiples; indication only — no magnetism; nothing in View mode [auto]
 - [ ] Lights toggle by default (v1.39.0): a device whose PRIMARY entity is a
       light (bulbs, chandeliers, night lights, light groups) toggles on click
       out of the box — no per-device setting needed; the device dialog shows