blocksStore.reorderBlock already existed but was never wired into the
editor, so sections could only be created or deleted — not moved. Adds
two arrows in the BlockInspector header next to the delete button.
- blocksStore: moveBlockUp / moveBlockDown helpers that look up the
block's siblings (same page + parent), compute the fractional index
that swaps with the neighbour, and delegate to reorderBlock
- BlockInspector: up / down buttons with disabled state at the bounds,
plus siblings prop driving canMoveUp / canMoveDown
- EditorView: derives selectedSiblings (same-parent blocks on the
current page) and passes them down
Works for top-level sections and for children inside containers,
since siblings are scoped to (pageId, parentBlockId).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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