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

package.json

@@ -1,6 +1,6 @@
 {
   "name": "houseplan-card",
-  "version": "1.37.3",
+  "version": "1.38.0",
   "description": "Interactive house plan Lovelace card for Home Assistant",
   "license": "MIT",
   "type": "module",