fix: Resolve test isolation and mypy type checking issues.

- Fix test_database_service.py fixture using wrong attribute name (_db_path instead of _database_path)
- Add proper SQLAlchemy imports (and_, desc) for type-safe query construction
- Replace .desc() method calls with desc() function and col() wrapper
- Fix join condition to use and_() instead of boolean operators
- Fix tuple access in select queries with multiple columns
- All 109 tests passing, mypy clean, no regressions

tests/unit/test_configurable_paths.py

@@ -106,6 +106,11 @@ class TestConfigurablePaths:
             # Set custom database path
             path_manager.set_database_path(test_db_path)
 
+            # Initialize database tables for the custom path
+            from leggen.services.database import init_database
+
+            init_database()
+
             # Test database operations using DatabaseService
             database_service = DatabaseService()
             balance_data = {