Fix close-path SQLite lock by releasing write lock before exchange/sim ops.

Also enable WAL and busy_timeout on get_db so concurrent sim writes wait instead of failing immediately.

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

app.py

@@ -1591,8 +1591,14 @@ def _purge_key_monitors_if_full_margin():
 
 
 def get_db():
-    conn = sqlite3.connect(DB_PATH)
+    # timeout/busy_timeout: 并发写(平仓握锁 + sim 再开库)时等待而非立刻 database is locked
+    conn = sqlite3.connect(DB_PATH, timeout=30)
     conn.row_factory = sqlite3.Row
+    try:
+        conn.execute("PRAGMA busy_timeout=30000")
+        conn.execute("PRAGMA journal_mode=WAL")
+    except Exception:
+        pass
     return conn