feat: add loopback host configuration for health checks

- Introduced LOOPBACK_HTTP_HOSTS in config.py to define valid loopback addresses for health-check URL and MINI_APP_SKIP_AUTH safety.
- Updated run.py to utilize LOOPBACK_HTTP_HOSTS for determining the host in health check and authentication logic.
- Enhanced test_app.py to skip tests if the required webapp output directory is not built, improving test reliability.

duty_teller/config.py

@@ -22,6 +22,9 @@ logger = logging.getLogger(__name__)
 # Valid port range for HTTP_PORT.
 HTTP_PORT_MIN, HTTP_PORT_MAX = 1, 65535
 
+# Host values treated as loopback (for health-check URL and MINI_APP_SKIP_AUTH safety).
+LOOPBACK_HTTP_HOSTS = ("127.0.0.1", "localhost", "::1", "")
+
 # Project root (parent of duty_teller package). Used for webapp path, etc.
 PROJECT_ROOT = Path(__file__).resolve().parent.parent