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>

kline_stream.py

@@ -102,8 +102,8 @@ class KlineStreamHub:
         if is_trading_session() and sub.period in FAST_PERIODS:
             return True
         try:
-            import sqlite3
-            conn = sqlite3.connect(db_path)
+            from db_conn import connect_db
+            conn = connect_db(db_path)
             ensure_kline_tables(conn)
             meta = load_meta(conn, chart_sym, sub.period)
             conn.close()