fix: correct storage usage calculation by using direct SQL query

The original implementation tried to find user's home folder via
file_repository.list_files(None), but this only returns files (not folders)
and folders are in a separate table. This resulted in storage always
showing 0 bytes.

Fixed by using a direct SQL query to sum file sizes by user_id from
storage.files table, which is more efficient (O(1) vs recursive) and
correctly calculates storage for all files owned by the user.

src/common/di.rs

@@ -398,7 +398,7 @@ impl AppServiceFactory {
     /// Creates the storage usage service (requires database)
     pub fn create_storage_usage_service(
         &self,
-        repos: &RepositoryServices,
+        _repos: &RepositoryServices,
         db_pool: &Arc<PgPool>,
     ) -> Arc<dyn crate::application::ports::storage_ports::StorageUsagePort> {
         let user_repository = Arc::new(
@@ -406,7 +406,7 @@ impl AppServiceFactory {
         );
         let service = Arc::new(
             crate::application::services::storage_usage_service::StorageUsageService::new(
-                repos.file_read_repository.clone(),
+                db_pool.clone(),
                 user_repository,
             ),
         );