beads: add a one-column stream layout beside the board

?layout=stream renders the same filtered set, the same buckets and the same
cards as one column of sections instead of four lanes side by side. It is a
layout of the Beads view and not a fifth tab: filters, the ready toggle, the
search box and ?issue= behave exactly as they do on the board.

A column read top to bottom can afford one sort per section, because each
section answers a different question: Rolling by started_at desc (what was
picked up last is what is being worked on), Lined Up ready-first then priority
then oldest, Stalled by blocker count (one blocker away is nearer than five),
Past Stand by closed_at desc. started_at and closed_at join the card model as
sort keys and are not displayed; a row missing one sorts last, because an unset
timestamp is not a very old one.

Past Stand opens collapsed in a <details> — the largest and least actionable
section, closed without a line of JavaScript. The sections are derived from the
finished lanes rather than bucketed again, so the section counts cannot drift
from the marquee, and the lanes keep the board order the board renders.

The Board/Stream toggle rebuilds the current query with layout replaced, via a
new withQuery template func, so every active filter survives the switch.