Point the alerting docs at the uptime runbook

[Babissimo]

docs/alerting.md described a dead-man's switch nobody had wired and told readers to add an UptimeRobot or Healthchecks.io monitor as an optional extra. The outside-in layer now exists (DigitalOcean Uptime checks, resource alerts and Cloudflare notifications, applied 2026-09-15 and recorded in claude-shared, offworldlabs/claude-shared#24), so the doc names that instead, marks the heartbeat task as dormant rather than implying it runs, and stops pointing an external probe at the strict readiness form. docs/runbook.md gets the matching one-line correction.

ClickUp: https://app.clickup.com/t/123zgec2z7a

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[claude]

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Review: Point the alerting docs at the uptime runbook

• Gather context (PR diff, prior review comment, CLAUDE.md)
• Read changed files in full
• Verify the "towers" hostname issue from the prior review, and check for other issues
• Post final review

The previously flagged issue is now fixed. docs/alerting.md:94-96 was updated to read:

DigitalOcean Uptime polls /api/health on api (this backend) and on towers (tower-finder-service's own edge) for prod and staging...

That parenthetical is exactly the clarification the prior review asked for — it now tells the reader up front that the towers check exercises tower-finder-service, not this backend, so nobody reading this doc will assume a towers.retina.fm failure means this repo's code is down. It's consistent with docs/architecture.md:15-17 (towers served from tower-finder-service's own edge) and with .github/workflows/ci.yml:1066-1107, which excludes towers.retina.fm from this repo's /api/health smoke checks for the same reason.

I re-checked the rest of the revision and found no other issues:

• backend/services/tasks/heartbeat.py:1-6 and health_monitor.py:9-12 both describe the heartbeat as dormant and point at claude-shared/docs/runbooks/uptime-monitoring.md (slash included) — matches the code (heartbeat_task no-ops when HEARTBEAT_URL is unset, and no environment sets it, per backend/.env.example:78-81).
• docs/runbook.md:252-254 and docs/alerting.md:147-149 agree that outside-in probes use the plain (liveness) /api/health form rather than ?strict=1.
• backend/.env.example:78-81's comment wraps consistently with its neighbors.
• ONBOARDING.md:299's one-line pointer update is accurate.

Nothing else stood out. This revision looks ready to merge.