Description
## Problem
`GET /api/v1/nodes/{id}` returns `provision_state: null` even when the YAML store has a valid provision state (e.g. `status: pending`). This makes it impossible to debug provisioning issues via the API.
Discovered during Brussels district enrollment — the web UI provision trigger was working (YAML store updated) but the API showed null.
## Fix
Ensure `provision_state` is correctly serialized in the node API response. Check if the Node struct serialization skips the field when the map is initialized but has entries.