Revert header to older version

[dusalex]

This PR reverts the header to a simpler design as requested in issue #2.

Changes:

• Remove "Course Materials Assistant" header text
• Remove subtitle about asking questions
• Remove horizontal border below header
• Keep theme toggle functionality
• Update page title to "Chat Assistant"
• Adjust CSS layout for minimal header design

Closes #2

Generated with Claude Code

[claude]

Code Review Feedback

✅ Positive Aspects

1. Clean Implementation: The changes successfully achieve the stated goal of simplifying the header design while maintaining essential functionality.

2. Consistent Changes: Both HTML and CSS modifications are well-coordinated - removing HTML elements and their corresponding styles.

3. Preserved Functionality: The theme toggle button remains fully functional and properly positioned.

4. Good CSS Cleanup: Removed unused styles (.header-text, header h1, .subtitle) that would otherwise become dead code.

📋 Code Quality Assessment

Structure & Organization: ✅ Good

• Changes follow the existing code structure
• Maintains proper CSS class hierarchy
• Clean separation of concerns

Semantic HTML: ✅ Maintained

• Header structure remains semantic
• Accessibility attributes preserved on theme toggle

🔍 Minor Considerations

1. Title Change Impact: The page title changed from 'Course Materials Assistant' to 'Chat Assistant' - ensure this aligns with the overall application branding strategy.

2. Layout Robustness: The header now only contains a right-aligned theme toggle. Consider if this creates any layout issues on very narrow screens or if additional header content might be added later.

3. CSS Version Cache: The stylesheet version remains at v=9 - consider incrementing to ensure cache invalidation across deployments.

🚀 Performance & Security

• Performance: ✅ Actually improves performance by reducing DOM elements and CSS rules
• Security: ✅ No security concerns - purely presentational changes
• Accessibility: ✅ Theme toggle maintains proper ARIA labels and keyboard navigation

📝 Suggestions

1. CSS Organization: The header section in style.css:133-146 is now quite minimal. Consider if this section could be consolidated or if comments should be updated.

2. Future Flexibility: If headers might need content again, consider keeping a placeholder structure or documenting the simplification decision.

🧪 Testing Recommendations

• ✅ Theme toggle functionality
• ✅ Responsive behavior on mobile devices
• ✅ Cross-browser compatibility
• ✅ Cache invalidation (if CSS version is updated)

Overall Assessment: ✅ APPROVED

This is a clean, focused PR that successfully implements the requested changes without introducing bugs or breaking existing functionality. The code quality is good and follows the project's conventions.