fix: handle zero entry_time in position sync and update gitignore

- Add fallback for zero/invalid entry_time when syncing positions
- Update .gitignore to ignore data/ directory and all .db files
- Remove accidentally committed nofx.db and image files

.gitignore

@@ -30,9 +30,12 @@ Thumbs.db
 # 环境变量
 .env
 config.json
-data.db*
 configbak.json
 
+# 数据目录（数据库、日志等）
+data/
+*.db
+
 # 决策日志
 decision_logs/
 coin_pool_cache/