Allow hiding Deck task lists from Tasks while keeping Calendar integration enabled

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Is your feature request related to a problem? Please describe.
When Deck's Calendar/CalDAV integration is enabled, Deck cards with due dates can be displayed in Nextcloud Calendar. This is very useful.

However, the same integration also exposes the Deck boards as task lists in the Nextcloud Tasks app, where they appear as lists such as Deck: .

For users who use Deck for project management and Tasks separately for personal or regular CalDAV tasks, this makes the Tasks sidebar unnecessarily cluttered. With multiple Deck boards, a large number of Deck: ... lists can appear in Tasks.

Currently, disabling the Deck Calendar integration is not a solution, because this also removes the useful integration of Deck card due dates with Nextcloud Calendar.

A similar request was previously reported in nextcloud/tasks#2456, but was closed there because Tasks was considered the wrong repository/component for this functionality:
https://github.com/nextcloud/tasks/issues/2456

Describe the solution you'd like
It should be possible to keep Deck's Calendar/CalDAV integration enabled while optionally preventing Deck-generated task lists from appearing in Nextcloud Tasks.

Ideally, Deck could provide separate settings for the two use cases, for example:

• Expose Deck cards/due dates to Calendar: enabled/disabled
• Expose Deck boards as task lists to Tasks: enabled/disabled

The desired configuration would then be:

• Deck → Calendar integration: enabled
• Deck cards with due dates visible in Calendar: yes
• Deck: lists visible in Tasks: no

Alternatively, if separating the CalDAV exposure itself is not technically feasible, it would be helpful if Deck exposed sufficient metadata so that the Tasks app could reliably identify and optionally hide Deck-provided task lists.

Describe alternatives you've considered
Disabling Deck's Calendar integration entirely.
This removes the Deck lists from Tasks, but also removes the desired Calendar integration for Deck cards with due dates.

Additional context
The goal is not to disable the Deck CalDAV integration altogether.
The important distinction is between two different user-facing use cases that currently seem to be coupled:

• Showing Deck cards with due dates in Nextcloud Calendar
• Showing Deck boards as task lists in Nextcloud Tasks

It would be useful if these could be controlled independently.

Start by tracing Deck's Calendar/CalDAV integration and how its boards become task lists in Nextcloud Tasks; the issue names no specific files or tests. Determine whether separate exposure settings or identifying metadata is feasible. Done means Calendar visibility for Deck card due dates can remain enabled while Deck-generated task lists are independently hidden.