Add permission check handlers for extensions

- Add check.rs with Tauri commands for checking web, database, and filesystem permissions
- Implement handlePermissionsMethodAsync in frontend to route permission checks
- Register permission check commands in lib.rs
- Add toast notification for permission denied errors in web requests
- Extensions can now check permissions before operations via SDK

src-tauri/src/extension/permissions/mod.rs

@@ -1,3 +1,4 @@
+pub mod check;
 pub mod manager;
 pub mod types;
 pub mod validator;