- Add header.templ component with app title, search, theme switcher, user menu
- Implement dropdown menus for theme selection and user actions
- Add wood theme options (Wood Light, Wood Dark, Wood Mahogany)
- Support all existing themes with visual color swatches
- Auto-close dropdowns when clicking outside
- TypeScript header functionality with proper type safety
Features:
- Left: App title "📚 Bookmann" linking to /bookshelf
- Center: Search box (ready for future search functionality)
- Right: Theme switcher button with color dropdown → User icon menu
- User menu includes Settings, Admin Panel (if admin), and Logout
- Theme persistence to localStorage and server via API
