ui: per-host Jobs sub-tab; drop unused Settings stub

Adds /hosts/{id}/jobs page listing recent jobs for the host (newest
first, capped at 100) with click-through to /jobs/{id}. Converts the
Jobs placeholder <div> to a real <a> nav link; removes the Settings
stub entirely. Also registers durationHuman template func and a
.jobs-row CSS grid to match the existing .schd-row idiom.

internal/server/http/server.go

@@ -195,6 +195,7 @@ func (s *Server) routes(r chi.Router) {
 			r.Get("/hosts/{id}/sources", s.handleUIHostSources)
 			r.Get("/hosts/{id}/sources/new", s.handleUISourceGroupNewGet)
 			r.Get("/hosts/{id}/sources/{gid}/edit", s.handleUISourceGroupEditGet)
+			r.Get("/hosts/{id}/jobs", s.handleUIHostJobs)
 			r.Get("/hosts/{id}/repo", s.handleUIHostRepo)
 			r.Get("/hosts/{id}/repo/trend", s.handleUIRepoTrend)
 			r.Get("/hosts/{id}/schedules", s.handleUISchedulesList)