refactor(ui): global code quality pass

refactor(ui): global code quality pass

- Fix ToggleButton.vue: replace unsafe for...in on localStorage with
  Object.keys(), cache localStorage value (4 reads reduced to 1)
- Extract 42-line inline @change handler in ChargingStationsView.vue
  to handleUIServerChange method
- Move ServerFailureError from WebSocketClient.ts to errors.ts
  (proper separation of concerns, re-exported for backward compat)
- Simplify useExecuteAction callback param: remove union type,
  use only ExecuteActionCallbacks object; update call sites
- Remove unnecessary String() in cli table.ts template literals