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

package.json

@@ -1,6 +1,6 @@
 {
   "name": "houseplan-card",
-  "version": "1.39.0",
+  "version": "1.40.0",
   "description": "Interactive house plan Lovelace card for Home Assistant",
   "license": "MIT",
   "type": "module",