refactor(tests): replace crud references with repo across repository test files

- Updated import statements and test logic to align with `repositories` naming changes.
- Adjusted documentation and test names for consistency with the updated naming convention.
- Improved test descriptions to reflect the repository-based structure.

backend/app/repositories/base.py

@@ -1,6 +1,6 @@
 # app/repositories/base.py
 """
-Base repository class for async CRUD operations using SQLAlchemy 2.0 async patterns.
+Base repository class for async database operations using SQLAlchemy 2.0 async patterns.
 
 Provides reusable create, read, update, and delete operations for all models.
 """