Refactor test cases for improved readability and consistency

- Updated test functions in various test files to enhance code clarity by formatting long lines and improving indentation.
- Adjusted assertions to use multi-line formatting for better readability.
- Added new test cases for theme settings API to ensure proper functionality.
- Ensured consistent use of line breaks and spacing across test files for uniformity.

models/role.py

@@ -0,0 +1,13 @@
+from sqlalchemy import Column, Integer, String
+from sqlalchemy.orm import relationship
+
+from config.database import Base
+
+
+class Role(Base):
+    __tablename__ = "roles"
+
+    id = Column(Integer, primary_key=True, index=True)
+    name = Column(String, unique=True, index=True)
+
+    users = relationship("User", back_populates="role")