swarm-ui: a builds page for the swarm builder's runs, and the status links to it

/builds lists the builder's recent builds newest first, one card each with how
it ended, and opens a failed build's nix tail. /builds?run=<id> opens that
build's card and scrolls to it. The swarm-builder commit status now links
there instead of to the raw JSON record.

frontend/packages/swarm-ui/src/shell/Shell.tsx

@@ -56,6 +56,7 @@ const NAV_ITEMS: { href: string; label: string; accent: string }[] = [
   { href: "/schedules", label: "schedules", accent: "var(--cyan)" },
   { href: "/issues", label: "issues", accent: "var(--yellow)" },
   { href: "/review", label: "review", accent: "var(--amber)" },
+  { href: "/builds", label: "builds", accent: "var(--green)" },
   { href: "/components", label: "components", accent: "var(--blue)" },
 ];