- Bug 1: shift-click now always adds the target card and sets it as the
last-selected anchor, so range selection works even when 0 or 1 cards
are selected.
- Bug 2: column select-all checkbox now toggles: if every card in the
column is already selected, clicking unselects them all.
- Bug 3: applyBulk now mirrors moveSelected with optimistic UI updates
for status moves and calls loadBoard() on catch for consistency.
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