feat v1.28.0: sub-area rooms — manual device placement without an HA area (issue #3)

- area-less rooms appear in the marker room list ('no area, manual'); markers
  store room_id and land at the room centre; dialog reopen restores the choice
- pure parseRoomRef (space#area / space#@roomId) + unit tests; backend schema
- ROADMAP phase 11 closed; TESTING.md row; smoke_subarea.mjs

custom_components/houseplan/manifest.json

@@ -16,5 +16,5 @@
   "issue_tracker": "https://github.com/Matysh/houseplan-card/issues",
   "requirements": [],
   "single_config_entry": true,
-  "version": "1.27.0"
+  "version": "1.28.0"
 }