ui+server: schedule next-run / last-run on dashboard + schedules tab

P2R-14. New store.LatestJobBySchedule query (per-schedule fired job).
Schedules-tab handler computes next-fire from cron + last-fire from
the jobs table per row. Schedules table grows two columns; dashboard
host row prepends 'next 12h ago/from now' to the existing last-backup
line when a single covering schedule is the run-now candidate.

Embeds store.Schedule into scheduleRow so existing template field
references keep working without bulk renames.

web/templates/partials/host_row.html

@@ -30,6 +30,9 @@
     {{- else -}}
       <span class="text-ink-fade italic">never run</span>
     {{- end -}}
+    {{- if .NextRun -}}
+      <br><span class="mono text-[10.5px] text-ink-fade" title="{{.NextRun.Format "2006-01-02 15:04:05 MST"}}">next {{relTime .NextRun}}</span>
+    {{- end -}}
   </div>
   <div class="text-right mono {{if eq $h.Status "offline"}}text-ink-mid{{else}}text-ink{{end}}">{{bytes $h.RepoSizeBytes}}</div>
   <div class="text-right mono {{if eq $h.Status "offline"}}text-ink-mute{{else}}text-ink-mid{{end}}">