Usabilty enhancements consistent with Nextcloud: Set start page and unsubscribe

DECK basically is great but in multiuser environments it can become overcrowded if the number of assigned decks becomes huge with some inconvenient consequences.

Some enhancements could resolve that:

1. Whenever one opens deck 'Upcoming cards' is shown. Depending on usage this may become nasty. There shoud be an option to set 'Upcoming cards', 'All board' or an individual board as startup page.

2. Unlike in calender it is not possible to hide shared decks. If there are many users with many boards and they all share with you as team leader things will get messed up. It would help a lot if there was not only a group 'All boards' and 'Shared with you' but also 'My boards'. 'My boards' might be an additional group or replace 'All boards'.

3. The option to 'Show boards in calender/tasks' should be individual for single boards. Having dozends or hundreds of shared boards in calendar/tasks is not really useful.

4. Also one should have the possibility to unsubscribe from shared boards as is in file-sharing to prevent being spammed from cloud users who think thier boards are important for you while you don't ...

Thanks and best
Nikolaus

Start by tracing the Deck UI entry points for the startup page, board grouping, calendar/tasks visibility, and shared-board membership. Clarify the desired settings and behavior for each of the four requests, then verify that preferences and unsubscribe actions work consistently across the affected views.