extract build-queue rollup as a shared Preact component

New @hive/shared/jobq-rollup.js (JobqRollup.tsx + jobq-rollup.css),
mirroring JobqGraph's shape exactly: JSX use plus an imperative
mountJobqRollup(container, props) for a plain-.js call site. Fetches
Vec<hive_jobq_wire::StateCount> off `endpoint`, sums Running+Finishing
roots as "running" and Pending roots as "queued", renders nothing when
both are zero. Optional `queueHref` adds a "view queue -> " link.

Swapped dashboard's hand-rolled queue-summary banner (swarm.js) over to
this component instead of keeping two parallel implementations - same
"one shared component" pattern JobqGraph already set for the rebuild
queue tree view. Mounted once into a new #jobq-rollup-section, kept as
a sibling of (not inside) #containers-section since that section gets
replaceChildren()-wiped on every container-state render, which would
tear down and remount a Preact tree on every tick. Refreshed via the
mount handle's .refresh() on rebuild_queue_changed, same as builds.js's
JobqGraph handle.

Also mounted in swarm-ui's /jobs page, above JobqGraph, with no
queueHref (a link back to the page you're already on is noise) - the
literal ask on hyperhive#3364.

Verified: npm run build (whole workspace) and swarm-ui typecheck both
clean, comment-block + issue-ref lints run manually, headless-chromium
screenshots of both the dashboard SW4RM tab and swarm-ui's /jobs page
against mocked /api/jobq/rollup payloads - banner renders identically
in both, with and without the queue link as expected.

frontend/packages/dashboard/src/dashboard.html

@@ -97,6 +97,13 @@
       <!-- Swarm / hive identity headline. Populated by refreshState from
            hive_name + swarm_name; stays hidden when neither is set. -->
       <h2 id="swarm-identity" hidden></h2>
+      <!-- JobqRollup mount point, kept outside #containers-section
+           deliberately — that section is wiped + rebuilt on every
+           container-list render (see swarm.js::renderContainers), which
+           would tear down and remount the Preact tree on every
+           container-state tick. Mounted once by swarm.js::initJobqRollup,
+           refreshed via its own handle rather than by re-rendering. -->
+      <div id="jobq-rollup-section"></div>
       <div id="containers-section">
         <p class="meta">loading…</p>
       </div>