migrate a gbfs feed from v2.3 to v3.0 without breaking existing consumers

Steps

1. Publish the new v3.0 feed set at a new path (e.g. /gbfs/3/) while keeping the existing v2.3 feed live at its current path, since GBFS versions are not interchangeable in place.
2. Update gbfs_versions.json to list both a "2.3" and a "3.0" entry with their respective feed URLs, and add manifest.json if you publish more than one city/system.
3. Convert renamed v3.0 fields: free_bike_status.json becomes vehicle_status.json, and bikes/bike_id/num_bikes_available/num_bikes_disabled become vehicles/vehicle_id/num_vehicles_available/num_vehicles_disabled.
4. Reformat data types required by v3.0: timestamps to RFC3339 strings, enum values to lowercase, prices in system_pricing_plans.json to non-negative floats (not strings), and phone numbers to E.164.
5. Populate the now-required feed_contact_email and a license_id or license_url in system_information.json, and add required opening_hours in OpenStreetMap format.
6. Validate both feeds with the GBFS Validator before publishing, and plan to keep the v2.3 feed live for about a year per MobilityData's migration guidance.