ux v1.38.0: binding section — radios + entities checkbox + dropdown

- Virtual / Pick-from-HA radios; Show-entities checkbox with tooltip
  gates device entities (groups/helpers always listed); searchable
  dropdown only in HA mode, auto-opens when empty, closes on pick;
  Save guarded until a binding is chosen; logic untouched
- smoke_binding_ui.mjs (16 checks); marker_stay/controls smokes green;
  TESTING/CHANGELOG same-commit

custom_components/houseplan/manifest.json

@@ -16,5 +16,5 @@
   "issue_tracker": "https://github.com/Matysh/houseplan-card/issues",
   "requirements": [],
   "single_config_entry": true,
-  "version": "1.37.3"
+  "version": "1.38.0"
 }