fix(traffic): сохранять историю и показывать достоверную свежесть

backend/drizzle/0011_traffic_collection_state.sql

@@ -0,0 +1,8 @@
+CREATE TABLE IF NOT EXISTS traffic_collection_state (
+  server_id BIGINT PRIMARY KEY REFERENCES servers(id) ON DELETE CASCADE,
+  server_updated_at TIMESTAMPTZ NOT NULL,
+  last_attempt_at TIMESTAMPTZ NOT NULL,
+  last_succeeded_at TIMESTAMPTZ,
+  status TEXT NOT NULL CHECK(status IN ('pending', 'ok', 'error')),
+  error TEXT
+);