feat(board): A board can be pinned as default board

[ramteid]

Adds a "Set as default board" option to the board context menu.

Opening Deck always navigated to the "Upcoming cards" overview, which is empty for teams that don't use due dates. With this change, any board can be pinned as the landing page: right-click it in the sidebar and choose Set as default board. The next time Deck is opened, it goes straight there. Choosing Remove as default board restores the normal overview.

The preference is stored in localStorage (key deck.defaultBoardId) with no server-side changes needed. The selection is wired through the Vuex store so that all board items in the sidebar stay in sync - pinning a new board immediately unpins the previous one everywhere.

• Resolves: [Feature request] Ability to change or pin default landing page Board #7658
• Target version: main

Open questions

English and German translations are available in this PR.
Will translation to missing languages be added by the Transifex pipeline automatically?

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Documentation (manuals or wiki) has been updated or is not required

[grnd-alt]

Thanks for this contribution! Nice to have this feature implemented.

[iFeedback]

Thank you, that was fast, really appreciate the support looking forward to see it.

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[magikmw]

right-click it in the sidebar and choose Set as default board.

@ramteid What do you mean, right-click? When I right-click I just get the Firefox right-click menu, nothing specific to Nextcloud or Deck.