修复持仓轮询时 SQLite database is locked 错误。

单连接复用并提交风控写入，启用 WAL 与 busy_timeout，缓存风控表 schema 初始化。

Co-authored-by: Cursor <cursoragent@cursor.com>

risk/account_risk_lib.py

@@ -76,7 +76,13 @@ def trading_day_reset_hour() -> int:
         return 8
 
 
+_SCHEMA_READY = False
+
+
 def ensure_account_risk_schema(conn) -> None:
+    global _SCHEMA_READY
+    if _SCHEMA_READY:
+        return
     conn.execute(
         """CREATE TABLE IF NOT EXISTS account_risk_state (
             id INTEGER PRIMARY KEY CHECK (id = 1),
@@ -93,6 +99,8 @@ def ensure_account_risk_schema(conn) -> None:
         conn.execute(
             "INSERT INTO account_risk_state (id, trading_day, manual_close_count, daily_frozen) VALUES (1, '', 0, 0)"
         )
+    conn.commit()
+    _SCHEMA_READY = True
 
 
 def _row_get(row, key, default=None):