A room can exist without a calendar, public API then reports it as free

[c0de111]

RoomVox 1.5.0, Nextcloud 34, PostgreSQL.

A room can end up without a calendar, and GET /api/v1/rooms/{id}/status then always answers free, whatever is booked. Nothing reports an error, so anything driving a room display or an automation off the public API shows the room as available.

To reproduce:

1. Create a room, e.g. office-103.
2. Delete it.
3. Create a room with the same ID again — the request fails with 500 (UNIQUE(principaluri, uri) on oc_calendars), but the room exists afterwards, without a calendar.
4. GET /api/v1/rooms/office-103/status returns free, and keeps returning free even with an accepted booking in place.