Update dependencies and add new features for improved functionality

- Updated Cargo.lock and Cargo.toml to include new dependencies
- Added new files for backup and watcher functionality in libmarlin
- Introduced integration tests and documentation updates
- Set workspace resolver to version 2 for better dependency resolution

libmarlin/src/db/mod.rs

@@ -1,6 +1,9 @@
 //! Central DB helper – connection bootstrap, migrations **and** most
 //! data-access helpers (tags, links, collections, saved views, …).
 
+mod database;
+pub use database::{Database, IndexOptions};
+
 use std::{
     fs,
     path::{Path, PathBuf},