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/api/src/books.rs

@@ -5,7 +5,7 @@ use sqlx::Row;
 use uuid::Uuid;
 use utoipa::ToSchema;
 
-use crate::{error::ApiError, AppState};
+use crate::{error::ApiError, state::AppState};
 
 #[derive(Deserialize, ToSchema)]
 pub struct ListBooksQuery {