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>

db_conn.py

@@ -0,0 +1,19 @@
+"""SQLite 连接统一配置（WAL + busy_timeout，降低并发锁冲突）。"""
+from __future__ import annotations
+
+import os
+import sqlite3
+
+DB_PATH = os.path.join(os.path.dirname(os.path.abspath(__file__)), "futures.db")
+
+
+def connect_db(path: str | None = None) -> sqlite3.Connection:
+    db_path = path or DB_PATH
+    conn = sqlite3.connect(db_path, timeout=30, check_same_thread=False)
+    conn.row_factory = sqlite3.Row
+    conn.execute("PRAGMA busy_timeout=30000")
+    try:
+        conn.execute("PRAGMA journal_mode=WAL")
+    except sqlite3.OperationalError:
+        pass
+    return conn