Add high-complexity PHPUnit tests: retry/backoff, auth guard, transactions, happy-paths, script state ...

- Refactor Base.php: extract executeCurl/getCurlInfo for mockability
- Refactor App.php: split api_auth_guard into check_api_auth (testable) + guard wrapper
- Refactor Devices.php: add optional ?Base DI to connect_new_device
- Update TestApp.php: add control_scripts_instances for script tests
- Update bootstrap.php: define PHPUNIT_TEST to skip new App() autoload side-effect

New test files:
- DeviceAPIBaseRetryTest (7 tests) — retry/backoff with mock cURL
- AppAuthGuardTest (7 tests) — auth + rate limiter without exit
- DevicesModelTransactionTest (4 tests) — happy path, rollback, mode checks
- AreasControllerHappyPathTest (7 tests) — full area CRUD success flows
- ScriptsModelStateTest (8 tests) — scope list, script state, enable/disable

Total: 113 tests, 285 assertions — all passing.