feat: bulk move cards and decks via multi-select closes: #162

[DevamPatel22]

Implements multi-select bulk operations in deck detail with long-press selection mode, checkboxes, and a bottom action bar (Move, Delete, Select All). Adds repository bulk APIs for cards/decks and corresponding tests for move/delete behavior.

[Pairadux]

Each deckRepo.delete() runs its own getDescendantIds() query + a separate transaction. With 10 selected decks, that is 10 transactions and 10 descendant lookups. CardRepository already has a bulkDelete that does it in one transaction — DeckRepository needs the same thing.

[Pairadux]

This overlays a checkbox at a fixed offset on top of the card. On narrow screens or long deck names, it will overlap content. Card items use an inline Checkbox inside the Row — deck items should do the same for consistency.

[Pairadux]

In selection mode, cards show a Checkbox on the left AND a check icon on the right. That is redundant — one indicator is enough.

[Pairadux]

Good work overall — three things to fix before merge:

1. Bulk deck delete is slow — deleteChildDecks loops over deckRepo.delete(), which runs a separate transaction + descendant query each time. Add a bulkDelete to DeckRepository (same pattern as CardRepository.bulkDelete) and call that instead.

2. Deck checkbox overlaps content — the Stack/Positioned checkbox floats on top of the deck card at a fixed offset. On small screens or long names it will cover text. Use an inline Checkbox in the row like the card items do.

3. Cards have two selection indicators — in selection mode, cards show a Checkbox on the left and a check icon on the right. Pick one.

I added comments to the lines themselves above ^