Overhaul system health section with job trigger controls and live timestamps

Rebuild the background jobs card as a sortable table showing each job's
schedule, last run time (live-updating via a new useTimeAgo hook), last
duration, and a manual trigger button backed by a new POST
/api/admin/jobs/trigger route. Extract StatusDot into a shared
component. Add cronToHuman() to display schedule patterns as readable
strings (e.g. "Every 6h", "Daily at 03:00"). Replace static
formatDistanceToNow calls throughout the health section with a
LiveTimeAgo component that refreshes every 30 seconds. Also swap a
handful of section icons for better visual matches across settings cards.

drizzle/20260305154106_regular_blockbuster/migration.sql

@@ -0,0 +1 @@
+ALTER TABLE `cronRuns` ADD `durationMs` integer;