feat: Cron management UI (view, toggle, trigger jobs from dashboard)

[vivekchand]

Inspiration

openclaw-dashboard has a cron management view that shows all scheduled jobs with toggle switches and manual trigger buttons.

What

Add a Cron Jobs panel to ClawMetry that shows all OpenClaw cron schedules per node:

• List all cron jobs with schedule, last run, next run, status
• Toggle enable/disable without editing config files
• Manual trigger — run a cron job on demand
• Execution history — see past runs with output/errors
• Multi-node view — see cron schedules across your fleet

Why

Cron jobs are invisible unless you SSH in and check. For fleet operators, knowing what's scheduled across all nodes (and being able to trigger/disable remotely) is a real ops need.

Implementation notes

• Sync daemon reads cron config from openclaw.json and reports to cloud
• Toggle/trigger commands sent back via WebSocket
• History stored in sync daemon's local DB, synced to cloud
• Show timezone per node (cron times can be confusing across zones)