Size the rail to what it carries

Stretched end to end, a panel with two dashboards showed a pill nine
tenths empty — which was tolerable while the rail was chrome outside the
canvas and obvious once it moved onto the panel itself. It now hugs its
entries and sits centred in the column it reserves; that column is the
same width either way, so no arrangement moves.

A rail longer than the panel is tall still scrolls, and still draws no
bar: a wall panel is swiped, and there is no room for one.

NOTEPAD.md

@@ -35,10 +35,6 @@ Deferring because out of scope is fine, but don't mention deferring than.
   (`ui/segmented.tsx`, `Common/RangePicker.tsx`, and the flow screens). The
   dashboard no longer shares them — it has its own, one per look — so
   unifying the remaining three is now purely an app-side job.
-- CHORE/UI: a panel's rail runs the full height of the canvas whatever it
-  carries, so two dashboards leave most of a tall pill empty. Hugging its
-  contents and centring would read better; the column it reserves stays the
-  same either way.
 - CHORE/UI: the house panels are laid out for 1280x800 — twelve columns, twelve
   rows. A chart's fixed chrome is now its legend alone: the range picker moved
   to a column down the right-hand edge and gave its row back, so a third chart