dashboard: the build pages are tabs of the dashboard

The build lifecycle used to be its own page with three sub-tabs. They are
now dashboard tabs (rebuild, meta, buildlogs) beside SW4RM and
P3RM1SS10NS: builds.js is a module tabs.js imports, so the dashboard's one
tab strip, /api/state snapshot and event stream (plus the meta_inputs_changed
and meta_update_running kinds) serve them, and the page, its bundle entry,
stylesheet and home tile are gone. The SW4RM banner's "view queue" link
points at the #rebuild tab, and the rebuild tab carries a count pill of the
rebuilds in flight.

An empty tab-count pill drew a "0": its display beat the UA [hidden] rule.

frontend/packages/dashboard/src/core.css

@@ -1,7 +1,6 @@
 /* ─── /core.html — C0R3 page ───────────────────────────────────────
    Kept state (tombstones) and stale permission entries. Section rules
-   imported from system-sections.css (shared with dashboard.css +
-   builds.css). */
+   imported from system-sections.css (shared with dashboard.css). */
 @import "./system-sections.css";
 
 body.core-shell {