feat v1.18.0: live segment ruler while drawing rooms + per-space scale

- Draw mode shows the current segment length near the cursor (metres or feet+inches
  per the HA unit system). New pure helpers segmentCm/formatLength (unit-tested).
- New per-space 'Scale (grid cell size)' field (space.cell_cm, default 5 cm) so each
  plan has its own real-world dimensions. i18n en/ru, .measurelabel style. +3 tests (61).

custom_components/houseplan/const.py

@@ -11,7 +11,7 @@ PLANS_DIR = "houseplan/plans"  # relative to the HA configuration directory
 FILES_URL = "/houseplan_files/files"
 FILES_DIR = "houseplan/files"
 CONF_ADMIN_ONLY = "admin_only"
-VERSION = "1.17.2"
+VERSION = "1.18.0"
 
 DEFAULT_CONFIG: dict = {
     "spaces": [],