feat: 任务详情 LLM 请求数（cost_records 存 completions）

cloud/db.py

@@ -961,6 +961,7 @@ POSTGRES_SCHEMA = (
     "usd_micros BIGINT, "
     "source TEXT, "
     "fallback_count INTEGER DEFAULT 0, "
+    "completions BIGINT DEFAULT 0, "
     "day TEXT, "
     "created_at DOUBLE PRECISION)",
     "CREATE TABLE IF NOT EXISTS oauth_states("