feat(web): Overview/Tables/Beads tab bar + full issue fields on beads detail

Give every database page a consistent three-tab bar — Overview, Tables,
then the applicable views (Beads) — in that order. Previously the bar only
carried [views, Tables] and the Overview page marked Tables active, so there
was no way to tell you were on the overview. viewtabs now takes an explicit
Current sentinel ("overview" | "tables" | view slug) and the tree/table row
pages render the bar too (handlers compute applicable views for the ref).

Surface the issue fields the beads detail pane was dropping. The closure
reason (close_reason) recorded by `bd close -r` was never shown; auditing
against bd's own field set also turned up estimated_minutes, external_ref,
spec_id, and started_at. All render conditionally, so issues that don't set
them stay uncluttered.

style(web): restyle the beads parade in the todo.sr.ht idiom

The board still read as a rounded-card kanban from another app. Re-skin
every surface in sourcehut's own issue-tracker language (todo.sr.ht):
flat and square — no border-radius, no shadows, no tints — hairline gray
borders, monospace ids, striped-on-hover rows instead of cards, and
squared bordered labels (the sourcehut .label: 1px border, no radius).
The summary becomes a flat hairline strip and each lane a squared column
with a 2px accent cap. The Mardi Gras hues survive only as small square
swatches and the lane cap, never as fills, so the view looks like a
native sourcehut tracker in both the light and dark themes. Verified via
a headless light/dark render. Test asserts the renamed summary class.

feat(web): Mardi Gras beads view

Render a beads (bd) issue database as a Mardi Gras parade board: four
lanes — Rolling (in progress), Lined Up (open & ready), Stalled (open &
blocked), Past Stand (done) — plus a marquee of per-lane counts. Cards
show id/title/type/priority/assignee/labels and blocked-by/blocks counts;
an issue-detail pane (?issue=<id>) shows the full issue with its
dependency edges in both directions and its comments thread.

Fingerprints on the issues + dependencies tables and reads everything
through the browse layer (column-name-keyed, so column order is
irrelevant), capped at 2000 rows/table. Status is bucketed via
custom_statuses with name heuristics as a fallback; "blocked" means
is_blocked or an open blocking dependency. Plugs into the view registry
via init()+RegisterView with no framework edits. Purple/gold/green
palette scoped in the template (no scss rebuild needed).