Add medium-complexity PHPUnit tests: Area recursion, controller validation ...

- AreaRecursionTest (10 tests): recursive traversal, depth limit ≤10,
  remove() cascade, inner devices/scripts lookup, parent_area()
- AreasRESTAPIControllerValidationTest (10 tests): new_area, update_alias,
  remove_area, place_in_area, update_display_name validation
- DevicesRESTAPIControllerValidationTest (12 tests): setup_new_device,
  do_device_action, update_alias, devices_list, place_in_area validation
- ScriptsRESTAPIControllerValidationTest (10 tests): run_action_script,
  set_*_state, place_in_area validation
- Fix Controller::validate_positive_int_ids() return type: ?array → ?string
- Add DevTools to TestApp/bootstrap for Model instantiation
- Expand bootstrap.php text_msgs with controller error aliases
- Update server-audit.md coverage table: 80 tests, 202 assertions