pane 0.2.0 — grids, row cursor, chart geometry

The domain-free curses layer under the PATE-stack TUIs. Stdlib only, no install step.

Everything here was driven by building catnip's redesigned views on top of this layer — the additions are the primitives that turned out to be missing, and the fixes are drawing faults that only showed up once real data hit them.

Added

• grids.py — heatmap() and ramp_glyph(). A rows × columns intensity grid, the complement to bar_chart: bars answer "how much over time, for one series", the grid answers "which series, on which day". Clips oldest columns rather than newest, so "now" always stays on screen.
• grids.scrollbar() — a vertical track and thumb for any scrollable pane. Draws nothing when everything fits, and never rounds the thumb away to zero, since a zero-height thumb says "no overflow" on a four-thousand-row list.
• grids.diverging_bars() — signed values above and below a zero line, for series where the sign is the finding rather than the magnitude.
• heatmap(header_gap=…) — blank rows between column labels and the first row.
• interact.RowCursor — a selection index plus the scroll offset that keeps it visible, with total/page supplied per call so one cursor survives a list that shrinks under it. The precondition for any list → detail drill-down.
• bar_chart(geometry=...) — an optional out-dict reporting the layout actually used. A caller annotating a chart cannot derive bar positions once binning and shrinking have run. Purely additive.

Fixed

• heatmap's glyph_for return value was repeated cell_w times, so marking one cell in a five-wide column emitted twenty-five characters and slid every later column out from under its header.
• heatmap column labels collided at the right edge, running two dates together as 0708-06. Labels are now walked newest-first and dropped rather than overlapped.
• A bar carrying both peak and value_labels had its value written over the marker, so a chart whose legend promised "▲ marks this day" drew none.

Vendoring

grids.py is a new module, so the byte-identity set (framework, charts, fmt, windows) is untouched. It is optional at every vendor site, like interact.py. catnip/src/catnip/tui is registered in tools/check-vendor.sh.

80 tests pass on 3.10 and 3.14.