web: answer what is ready across every tracker

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.

beads: drop the Bead/Beads prefix from the moved types

beads: extract the projection out of web/

web/beads.go held the one reading of the beads schema — the table
fingerprint, the lane bucketing, the ready rule, the status categories,
the transitive dependency walk, the event humanizer, the filter model and
the milestone rollup — where a second consumer could not reach it. The
MCP surface and the cross-database ready page both need it.

Move it to a new root package beads/ that depends on browse/ and the
standard library only: rows in, view model out, no net/http, no
html/template, no core. The BrowseSession seam is declared consumer-side
there and names the one method the projections call, so web's larger
BrowseSession satisfies it structurally and a session passes straight
through.

web/beads.go and web/milestones.go keep only their View adapters — slug,
label, template, Applies, and the hand-off of ref and query. The
templates are unchanged: the moved types keep their names and their
display methods, so every dot still resolves.

Pure move plus the beadsMax -> beads.Max export rename. The projection
tests move with the code and become testify; the render tests stay in
web/ unchanged. Same 63 tests pass before and after.