Add unit tests for SettingsForm class (COG-37)

Summary

This PR implements comprehensive unit tests for the SettingsForm class as requested in COG-37. The implementation adds three test methods that verify form validation behavior and the save() method's commit parameter functionality:

• test_form_invalid_missing_fields: Validates that the form correctly rejects submissions with missing required fields (email, name) and returns appropriate error messages
• test_form_valid_saved_not_committed: Tests form.save(commit=False) to ensure it creates a User instance without persisting to the database
• test_form_valid_saved_and_committed: Tests form.save(commit=True) to verify the instance is both created and saved to the database

All tests follow Django testing best practices and integrate seamlessly with the existing test suite.

Review & Testing Checklist for Human

• Verify SettingsForm usage pattern: Confirm whether SettingsForm is intended to create new users (as tested) or update existing user settings. The current tests create new User instances rather than updating existing ones.
• Validate field requirements: Check that email and name are actually required fields by testing the SettingsForm directly in the Django admin or web UI. The tests assume these are required based on the model definition.
• Test password handling edge cases: Verify form behavior when password field is empty/None, since it's marked as required=False but the tests always provide a password value.
• End-to-end verification: Test the actual user settings functionality in the web application to ensure the test assumptions match real-world usage patterns.

Notes

• All existing tests continue to pass (16/16 tests successful)
• Test data uses realistic field values including valid email formats and URLs for the image field
• Tests verify both form validation and database persistence behavior as specified in the requirements

Session Details:

• Requested by: Jude Partovi (@jpartovi)
• Link to Devin run: https://app.devin.ai/sessions/f8b230ce60ff4ef8bdfa09cc1cee25cf