refactor: update AppState references to use state module

- Change all instances of AppState to reference the new state module across multiple files for consistency.
- Clean up imports in auth, books, index_jobs, libraries, pages, search, settings, thumbnails, and tokens modules.
- Simplify main.rs by removing unused code and organizing middleware and route handlers under the new handlers module.

apps/indexer/Cargo.toml

@@ -4,6 +4,8 @@ version.workspace = true
 edition.workspace = true
 license.workspace = true
 
+[lib]
+
 [dependencies]
 anyhow.workspace = true
 axum.workspace = true