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.

lib/db/schema.ts

@@ -350,6 +350,7 @@ export const cronRuns = sqliteTable(
     }).notNull(),
     startedAt: int("startedAt", { mode: "timestamp" }).notNull(),
     finishedAt: int("finishedAt", { mode: "timestamp" }),
+    durationMs: int("durationMs"),
     errorMessage: text("errorMessage"),
   },
   (table) => [