v1.7.0

New: admin-only HTTP liveness checks.

- Configure target URLs (with per-target interval, min 30s) from
  Settings → HTTP 檢測. Never surfaced on the public dashboard.
- Non-2xx / unreachable fires the existing Telegram/webhook channel via
  lib/notify — no separate token to manage.
- Dedup: notifications fire ONLY on up↔down state transitions. First
  check after a target is added records baseline silently. Sustained-down
  stays silent after the initial alert (no repeat spam).
- HEAD probe with GET fallback for sites that 403/405 HEAD; 8s timeout.
- Per-row "Test" button in the UI probes once and sends a synthetic
  notify so operators can verify the pipeline without bringing a real
  target down (does not touch persisted state).
- Config + state stored encrypted in app_settings.httpChecks
  (SENSITIVE_KEYS — URLs frequently carry auth tokens).