Scrutiny SMART metrics in Grafana via scrutiny-exporter + alloy scrape pipeline

## Summary
Surface scrutiny's SMART data in Grafana by running a scrutiny-exporter and scraping it with alloy.

## Motivation
Scrutiny stores SMART in its own InfluxDB with no Prometheus endpoint; alloy can't read it directly. jianyun8023/scrutiny-exporter reads scrutiny's API -> /metrics, with a ready-made Grafana dashboard + alert rules. SMART is already re-enabled on the drives, so this is unblocked.

## Scope
- Deploy scrutiny-exporter as a separate container (custom app), pointed at scrutiny's published API (node IP:31054). It can't embed in scrutiny (fixed omnibus image).
- alloy `prometheus.scrape` of the exporter -> Grafana, as a Terraform Fleet Management pipeline.
- Import the project's dashboard + alert rules.

## Acceptance criteria
- [ ] scrutiny-exporter running and reachable.
- [ ] SMART metrics in Grafana with the dashboard + alerts.

Blocked by #150 (Fleet Management foundation).