Added: Sheets — turn a bullet and its children into a spreadsheet-style grid, a
typed field table, or a Kanban board, with formulas, filters, aggregates,
group-by, and CSV/TSV import, all stored as plain Logseq Markdown; Split view
with per-pane tabs and history; Org-mode graphs; and an in-app Guide. Fixed:
backups now include nested pages; PDF highlight migration can't overwrite
another PDF's data; `##` headings render on every line; typing in a very long
block no longer jumps the caret.
