Add comprehensive test coverage for SettingsForm component

Summary

Adds complete test coverage for the SettingsForm component that was previously untested. The PR includes two new test classes:

• TestSettingsForm (11 tests): Comprehensive form validation testing including valid/invalid data scenarios, required field validation, email format validation, duplicate email handling, and form save functionality with proper password hashing
• TestSettingsView (5 tests): Integration testing of the settings view including authentication requirements, HTMX response handling, and proper template rendering

All tests follow existing codebase patterns using setUpTestData(), http.HTTPStatus assertions, and HTMX header validation. The implementation covers all form fields (email, name, bio, image, password) and edge cases like empty password handling.

Review & Testing Checklist for Human

• Verify HTMX integration works end-to-end: Navigate to /settings/ while logged in, submit valid form data, and confirm the HX-Redirect header properly redirects to the user profile page
• Test form validation behavior manually: Try submitting the settings form with invalid email formats, duplicate emails, and empty required fields to ensure the test assertions match actual form behavior
• Verify authentication requirements: Confirm that unauthenticated users are properly redirected when accessing /settings/ (both GET and POST requests)

Notes

• All 29 tests in the accounts module are passing, including the new test coverage
• The tests cover all specified requirements from the original task: form validation, save functionality, and view integration
• Password handling logic is tested for both cases: when provided (should be hashed) and when empty (should remain unchanged)

Link to Devin run: https://app.devin.ai/sessions/45cae496c7f54de7b0aefa4bcae3d848
Requested by: Jude Partovi (@jpartovi)