dashboard: replace <hive-jobq-graph> with a shared Preact component

Ports the shadow-DOM <hive-jobq-graph> custom element
(frontend/packages/shared/src/jobq-graph/) to a Preact component
(JobqGraph.js) shared by the dashboard and swarm-ui, per hyperhive#3310.

- JobqGraph.js: written with plain h() calls (no JSX) so the same file
  compiles unmodified under both the dashboard's text-loader CSS config
  and swarm-ui's JSX config. Exports `JobqGraph` for JSX use and
  `mountJobqGraph(container, props)` for the dashboard's non-JSX
  imperative mount, returning a `{refresh(), update()}` handle matching
  the old custom element's public surface. Same rendering contract as
  before: indented state tree, payload.label verbatim, payload.data as
  a generic key/value list, "waits on: <label>" text for Node-kind deps,
  per-state filter checkboxes, optional cancel button.
- jobq-graph.css: light-DOM adaptation of the old shadow-scoped
  stylesheet (:host -> .jg-root, otherwise unchanged).
- dashboard/src/builds.js: local mountJobqGraph() renamed to
  mountRebuildQueue() to avoid colliding with the newly-imported shared
  mountJobqGraph; cancel handling is now a plain onCancel callback
  instead of a DOM CustomEvent listener (no shadow boundary to cross
  anymore).
- dashboard + shared package.json: added preact as a dependency (matches
  swarm-ui's existing pin, 10.29.8) - the dashboard was a vanilla-JS MPA
  with no Preact/JSX pipeline before this.
- Removed the old hive-jobq-graph.js/.css entirely (confirmed via grep
  it had exactly one consumer, dashboard/src/builds.js, so this is a
  clean swap, not parallel maintenance of two implementations).
- Updated stale doc-comment references to the old element name in
  builds.html, tabs.js, swarm.js, docs/web-ui/dashboard.md, and
  hive-c0re/src/job_queue/mod.rs.

Verified: npm run build (whole frontend workspace) and npm run
typecheck (swarm-ui) both clean; cargo build/clippy/test -p hive-c0re
all clean (331 tests, 0 failures); headless-chromium screenshot of
/builds.html against a mock GET /api/jobq/graph payload confirms full
visual/behavioral parity with the old custom element (tree, filter
checkboxes, cancel buttons, error text, waits-on line, data list, live
build log panel).

This covers the dashboard-replacement half of hyperhive#3310 only. The
swarm-ui half (rendering the CreateAgent DAG on the agent-creation page)
is downstream of hyperhive#3306/#3124 landing - no swarm-ui page exists
yet to mount it in.

frontend/packages/dashboard/src/builds.css

@@ -9,6 +9,7 @@
    (`.builds-shell` body); only the build-logs-* component rules are used. */
 @import "./system-sections.css";
 @import "./logs.css";
+@import "@hive/shared/jobq-graph.css";
 
 body.builds-shell {
   margin: 0;