SQLite 改写 query planner，复杂连接快 4 倍 SQLite rewrites query planner: 4× on complex joins

NGQP+ reorders joins by selectivity, biggest wins on 7+ table queries; ATTACH cost model fixed. Notion-style nested queries see the largest gains.

NGQP+ 按选择度重排连接顺序，对 7 表以上查询特别明显，ATTACH 数据库成本模型也修了。Notion 风格嵌套查询提升最显著。