Prometheus metrics scrape endpoint

Returns the authenticated project's checks as Prometheus gauges in Prometheus text exposition format 0.0.4.

Metrics emitted (per check, labelled id, name, slug):

• lastping_check_up — 1 if status is up, else 0
• lastping_check_state{state="up|late|down|new"} — one-hot gauge for current state
• lastping_check_last_ping_timestamp_seconds — unix seconds of last ping (omitted when never pinged)
• lastping_check_due_timestamp_seconds — unix seconds of next expected ping (omitted if null)
• lastping_check_grace_seconds — grace period in seconds
• lastping_check_paused — 1 if paused, else 0
• lastping_checks — count of checks in the project

Authentication: accepts either X-Api-Key: lp_… or Authorization: Bearer lp_… (the Bearer form is provided specifically for Prometheus scrape_config).

Example Prometheus scrape_config:

scrape_configs:
  - job_name: lastping
    scrape_interval: 60s
    authorization:
      credentials: lp_YOUR_API_KEY
    static_configs:
      - targets: [app.lastping.dev]
    metrics_path: /api/v1/metrics
    scheme: https