fix: 盘中脚本统一使用get_conn()替代raw sqlite3.connect防DB死锁

- mofin_health.py, cron_health_monitor.py, intraday_health_check.py,
  self_todo_executor.py: 替换raw sqlite3.connect() → get_conn()
  统一使用WAL模式+busy_timeout=30s连接
- mofin_db.py: get_conn()每次新建连接时WAL checkpoint
  防止被kill进程残留WAL导致后续全部卡死
- 并发测试验证: 3x price_monitor + 3x mofin_health同时运行
  6/6通过，WAL仅32bytes

关联问题: 2026-07-14 SQLite写锁死锁根因诊断

scripts/self_todo_executor.py

@@ -5,9 +5,10 @@
 成功→completed。失败→调gateway API，带完整上下文让知微处理。
 """
 
-import json, sqlite3, subprocess, time, urllib.request
+import json, subprocess, time, urllib.request
 from pathlib import Path
 from datetime import datetime
+from mofin_db import get_conn
 
 BASE = Path("/home/hmo/MoFin")
 DB_PATH = BASE / "data" / "mofin.db"
@@ -28,8 +29,7 @@ def send_xmpp(msg):
 
 def main():
     start = time.time()
-    conn = sqlite3.connect(str(DB_PATH))
-    conn.row_factory = sqlite3.Row
+    conn = get_conn()
 
     rows = conn.execute(
         "SELECT id, title, description, fix_action FROM todos WHERE status='pending' "