Add test UI toggle and docs

app/config.py

@@ -6,9 +6,17 @@ from dotenv import load_dotenv
 load_dotenv()
 
 
+def _env_bool(name: str, default: bool = False) -> bool:
+    value = os.getenv(name)
+    if value is None:
+        return default
+    return value.strip().lower() in {"1", "true", "yes", "on"}
+
+
 @dataclass(frozen=True)
 class Settings:
     env: str = os.getenv("ENV", "prod").strip().lower()
+    test_ui_enabled: bool = _env_bool("FACE_LOCK_TEST_UI", True)
     auth_token: str = os.getenv("FACE_LOCK_AUTH_TOKEN", "").strip()
     auth_header_name: str = os.getenv("FACE_LOCK_AUTH_HEADER", "X-API-Key").strip()