进一步修复 SQLite 并发锁冲突，统一连接与重试机制。

新增 db_conn 模块、缓存 schema 初始化、positions 页 commit，风控读库自动重试。

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

strategy/strategy_db.py

@@ -116,7 +116,13 @@ CREATE TABLE IF NOT EXISTS ctp_sim_positions (
 """
 
 
+_TABLES_READY = False
+
+
 def init_strategy_tables(conn) -> None:
+    global _TABLES_READY
+    if _TABLES_READY:
+        return
     for sql in (
         ROLL_GROUPS_SQL,
         ROLL_LEGS_SQL,
@@ -129,3 +135,5 @@ def init_strategy_tables(conn) -> None:
         conn.execute(sql)
     if not conn.execute("SELECT id FROM ctp_sim_account WHERE id=1").fetchone():
         conn.execute("INSERT INTO ctp_sim_account (id, balance, available) VALUES (1, 100000, 100000)")
+    conn.commit()
+    _TABLES_READY = True