v1.2.4: collapsible help section in scenario editor modal

scenario-form.js: <details> block between name and steps:
- How steps work (operation → target)
- Create: service + output name
- Non-create: instance from scenario or cloud
- Parameters: key=value format with example
- Buttons: ↑↓ reorder, ✕ delete

site/app.py

@@ -19,7 +19,7 @@ from routes.api_scenario_run import bp_run as api_scenario_run_bp
 from routes.api_scenario_defs import bp_defs as api_scenario_defs_bp
 
 # Версия — меняется при КАЖДОМ изменении кода. Показывается в топбаре UI.
-VERSION = "1.2.3"
+VERSION = "1.2.4"
 
 app = Flask(__name__, template_folder="templates", static_folder="static")
 app.config["NUBES_API_ENDPOINT"] = os.getenv("NUBES_API_ENDPOINT", "https://lk-api-gateway-test.ngcloud.ru/api/v1/svc")