v1.10.0 — Health/staleness alerts

✨ Added

• Health/staleness monitoring (Layer 2 of the anomaly-alerting system). A new hourly check watches whether each metric's live data is still arriving at all — catches a stalled poller or an unreachable meter, independently of the poller itself. A metric with no live-data history (nothing configured for it) is never checked. Uses the same Telegram/banner delivery as the water leak alerts added in v1.8.0.
• Self-hosted: new health-check service in docker-compose.yml.

🐛 Fixed

• The leak-alert acknowledge endpoint could have applied the "not a leak" threshold adjustment to the wrong setting if a health alert happened to share the same metric name as a leak alert. Fixed before it could ever reach a real deployment.