fix v1.21.2: space-dialog polish

- scale (cm/cell) input compact again (generic width:100% dialog rule stretched it)
- space with no background image gets a white paper canvas (.stage.noplan), so
  hand-drawn rooms read like a plan on paper
- TESTING.md updated in the same commit

package.json

@@ -1,6 +1,6 @@
 {
   "name": "houseplan-card",
-  "version": "1.21.1",
+  "version": "1.21.2",
   "description": "Interactive house plan Lovelace card for Home Assistant",
   "license": "MIT",
   "type": "module",