feat(services): считать сервис живым при одном OK и писать историю failover

Сервис up, если жив хотя бы один IP. Failover показывает Down по FQDN и журнал add/remove A-записей.

Co-authored-by: Cursor <[email protected]>

packages/db/migrations/025_failover_log.sql

@@ -0,0 +1,11 @@
+CREATE TABLE failover_log (
+  id INTEGER PRIMARY KEY AUTOINCREMENT,
+  service_id INTEGER NOT NULL REFERENCES services(id) ON DELETE CASCADE,
+  binding_id INTEGER NOT NULL REFERENCES service_bindings(id) ON DELETE CASCADE,
+  fqdn TEXT NOT NULL,
+  ip TEXT NOT NULL,
+  action TEXT NOT NULL CHECK (action IN ('added', 'removed')),
+  created_at TEXT NOT NULL DEFAULT (datetime('now'))
+);
+
+CREATE INDEX idx_failover_log_service ON failover_log(service_id, created_at DESC);