WP-10: contract and failing tests for OS and package inventory

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

backend/crates/application/src/lib.rs

@@ -1,11 +1,13 @@
 //! Application layer: use cases orchestrating the domain through its ports.
 pub mod auth_service;
+pub mod inventory_service;
 pub mod jobs;
 pub mod scheduler;
 pub mod settings_service;
 pub mod user_service;
 
 pub use auth_service::AuthService;
+pub use inventory_service::{InventoryService, PackageRefreshJob};
 pub use jobs::{JobHandler, JobLog, JobRunner};
 pub use settings_service::SettingsService;
 pub use user_service::UserService;