Add od-backup-schedule runbook + od-backup-check script: schedule & monitor backups

Automate the nightly cold backup (Task Scheduler, filled-in local copy in
private tier), stagger the off-site upload, and MONITOR with three layers:
Task Scheduler last-run, a read-only health check (freshness/completeness/
size), and a dead-man's-switch heartbeat that pings an external monitor only
on success so silent failures and offline servers get caught. od-backup-check.ps1
is read-only (no DB/service), iex-safe, and pings <HEARTBEAT_URL> on PASS.
Cross-linked with od-db-backup.md and od-backup-verify.md; README updated.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

od-db-backup.md

@@ -106,6 +106,8 @@ Register the cold backup as a nightly **Task Scheduler** job (runs off-hours, as
 schtasks /Create /TN "OD Nightly Cold Backup" /TR "powershell -NoProfile -ExecutionPolicy Bypass -File C:\ops\od-db-backup-local.ps1" /SC DAILY /ST 23:30 /RU SYSTEM /RL HIGHEST
 ```
 
+Full scheduling **and monitoring** (staggering the off-site upload, a daily health check, and a dead-man's-switch heartbeat so a silent failure gets caught): **[`od-backup-schedule.md`](od-backup-schedule.md)**.
+
 ## 5. Verify — a backup you haven't restored is a guess
 
 - **Test-restore** to an **isolated** machine periodically (matching Open Dental + MySQL/MariaDB versions): `net stop`, rename the existing `opendental` folder aside, drop in the backup's `data\` contents, `net start`, launch Open Dental, spot-check patients/images. Full step-by-step with a health checklist: **[`od-backup-verify.md`](od-backup-verify.md)** (isolated Hyper-V test-restore).