Cron watchdog — Telegram alert for overdue tasks

OVERRIDES runtime profile: uses notify.py (urllib direct Telegram) because this watchdog never invokes the claude CLI — pure HTTP poll + alert.

Every 30 min, hits MC's /api/v1/scheduler/inspect and alerts Telegram (MC forum topic) for any task overdue by more than 2× its cron interval. Skips tasks marked disabled or runtime_profile: manual. Dedup'd per task at 1-hour cadence so a stuck task pings at most once per hour.

Complements scheduler-watchdog.md (creates MC tickets for various failure modes) — this one is the fast Telegram side-channel so Elmar sees stuck schedules within a single cycle rather than at the next hourly watchdog tick.

Implementation: ~/workspace/scripts/cron_watchdog.py. Ticket: MC-3306.