feat(db): 内容库迁入 SQLite，分类与侧栏导航改为数据库驱动

src/lib.rs

@@ -1,10 +1,12 @@
 pub mod config;
+pub mod db;
 pub mod error;
 pub mod listing;
 pub mod server;
 mod watcher;
 
 pub use config::Config;
+pub use db::Db;
 pub use error::StashError;
 pub use listing::{AppProject, scan_projects};
 pub use server::{ServerHandle, start};