Replace vehicle field settings

Creates, updates, reorders and deletes custom field definitions and updates the optional-field visibility toggles in one call.

custom_fields is the complete list: an entry with id updates that field (values stored on vehicles are kept), an entry without id creates one (the id is returned), an existing field left out is deleted. Array position is the display order. When custom_fields is absent the definitions are left unchanged.

Omitted attributes are kept, never reset: an absent field_visibility key keeps its toggle, and an absent visible or reminder_days_before on an existing field keeps its stored value. New fields default to visible: true and no reminder.

A hidden field creates no agenda events whatever its reminder_days_before says; the value stays stored and applies again once the field is shown. Likewise, with field_visibility.next_inspection_date set to false no revisione events are created. Events already in the agenda are never touched here.

Returns 422 parameter_invalid (with param pointing at the entry) for an unknown or repeated id, a repeated name (case-insensitive), a name outside 2–30 characters, an unknown type or more than 10 fields.