enable prefect V2 UI via PREFECT_SERVER_UI_V2_ENABLED
Opt into the experimental V2 UI bundled in prefect >=3.6.9. The V2
assets are already packaged in prefecthq/prefect:3.6.23-python3.11
(the image we're running) — this setting just switches the server's
static-file serving from the V1 bundle to the V2 bundle.
Reference: prefecthq/prefect#20065 (Alex Streed, merged Dec 31 2025) —
added V2 UI packaging to the Dockerfile and the server.ui.v2_enabled
setting that chooses which bundle FastAPI mounts. When v2_enabled is
true, create_ui_app uses prefect.__ui_v2_static_path__ and logs
"Serving experimental V2 UI" at startup.