0.17.0

0.17.0 — Excel-style per-column filters

• Every column header now carries a funnel button. Clicking it opens a filter dropdown for that
  one column, without going through the stacked-filters modal.
• The dropdown lists the column's distinct values with a count each, plus (Blanks), a
  (Select all) toggle, and a search box that narrows the list (with (Select all matching) while
  a search is active). Ticking and unticking applies immediately.
• List-valued properties contribute one entry per element, so a tags column offers each tag as its
  own checkbox rather than the joined string.
• Each dropdown also carries Sort A→Z / Z→A and a condition row — contains, is,
  is not, >, <, ≥, ≤, is empty, is not empty — for filters that a checkbox list can't
  express.
• A filtered column's funnel is highlighted, and the status line reports how many column filters are
  in force.
• Filters compose: stacked conditions run first, then formulas are evaluated, then the per-column
  filters, then the toolbar's quick search. Formula and heading columns are filterable on their
  rendered text.
• Following Excel, each dropdown's value list reflects the other columns' filters but not its own,
  so a value you just excluded is still there to re-tick.
• Mod+Shift+L toggles the filter buttons off and on. Turning them off clears the column filters —
  that is the point of the toggle in Excel — and the whole toggle is undoable with Mod+Z.
• New commands: Grid: toggle column filter buttons and Grid: clear all column filters. The
  column header's context menu gained Filter this column… and Clear all column filters.
• Internal: the scalar comparison used by formula conditions is now shared with the column filters,
  so both agree on numeric-vs-text and case-insensitive matching.