style: apply black and isort formatting across entire codebase

- Standardize quote style (single to double quotes)
- Reorder and group imports alphabetically
- Fix line breaks and indentation for consistency
- Apply PEP 8 formatting standards

Also updated Makefile to exclude both venv and .venv from code quality checks.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

tests/fixtures/auth_fixtures.py

@@ -53,6 +53,7 @@ def test_admin(db, auth_manager):
     db.expunge(admin)
     return admin
 
+
 @pytest.fixture
 def another_admin(db, auth_manager):
     """Create another test admin user for testing admin-to-admin interactions"""
@@ -72,6 +73,7 @@ def another_admin(db, auth_manager):
     db.expunge(admin)
     return admin
 
+
 @pytest.fixture
 def other_user(db, auth_manager):
     """Create a different user for testing access controls"""