- Hamburger button with animated X toggle (CSS-only icon)
- Slide-down mobile nav on ≤900px with 44px+ tap targets
- Semi-transparent overlay when menu is open
- Escape key + outside click + link click closes menu
- Auto-close on resize to desktop
- Desktop navigation unchanged
- Pure vanilla JS toggle, no jQuery dependency
- Generate mailto: link with all form data on submit
- Opens user's email client with pre-filled email to mki@kies-media.de
- Subject includes interest type, body contains all form fields
- Update success message to reflect email client behavior
- Remove fake setTimeout simulation
Fix#15
