Add comprehensive test coverage for services and utilities

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

src-tauri/src/repository/hybrid.rs

@@ -552,6 +552,10 @@ mod tests {
         async fn get_items_by_person(&self, _person_id: &str, _options: Option<GetItemsOptions>) -> Result<SearchResult, RepoError> {
             unimplemented!()
         }
+
+        async fn get_similar_items(&self, _item_id: &str, _limit: Option<usize>) -> Result<SearchResult, RepoError> {
+            unimplemented!()
+        }
     }
 
     /// Mock online repository that returns predefined items
@@ -677,6 +681,10 @@ mod tests {
         async fn get_items_by_person(&self, _person_id: &str, _options: Option<GetItemsOptions>) -> Result<SearchResult, RepoError> {
             unimplemented!()
         }
+
+        async fn get_similar_items(&self, _item_id: &str, _limit: Option<usize>) -> Result<SearchResult, RepoError> {
+            unimplemented!()
+        }
     }
 
     fn create_test_item(id: &str, name: &str) -> MediaItem {