feat: Integrate HTML templates with FastAPI
- Created template_helpers.py for centralized template rendering
- Added ux_features.css for enhanced UX styling
- Implemented JavaScript modules for:
- Keyboard shortcuts (Ctrl+K, Ctrl+R navigation)
- User preferences persistence
- Undo/redo functionality (Ctrl+Z/Ctrl+Y)
- Mobile responsive features
- Touch gesture support
- Accessibility features (ARIA, focus management)
- Screen reader support
- Color contrast compliance (WCAG)
- Multi-screen support
- Updated page_controller.py and error_controller.py to use template helpers
- Created comprehensive template integration tests
- All templates verified: index.html, login.html, setup.html, queue.html, error.html
- Maintained responsive layout and theme switching
- Updated instructions.md (removed completed task)
- Updated infrastructure.md with template integration details