Option to suppress native calendar provisioning when integration_davc is the calendar backend

Use case

Deployments using integration_davc against a central CalDAV server (e.g. Radicale) as the single source of truth. In this topology Nextcloud's native SabreDAV calendar layer (oc_calendars / default "Personal" calendar provisioning) serves no purpose, but it still exists alongside the DAVC calendars in the UI. Users can accidentally create events in the native local calendar, which then exist nowhere on the central server, invisible to every other client, leading to silent data fragmentation.

Request

A per-instance (or per-service) setting: when a DAVC connection is active for a user:
(a) suppress creation of the default native calendar, or;
(b) hide native calendars from the Calendar app UI, or minimally;
(c) let the admin mark DAVC calendars as the default write target.

Any of the three would prevent the split-brain.

Environment: Nextcloud 33.x, integration_davc 1.0.4, Radicale 3.7.4.

No file or test is named. Start by tracing how integration_davc handles an active DAVC connection and how Nextcloud's native SabreDAV calendar layer provisions the default Personal calendar. Done means a selected per-instance or per-service behavior prevents users from writing to an unshared native calendar, with coverage for the requested topology.