feat: mobile-first redesign (design-taste-frontend)

- responsive nav: compact sticky topbar + bottom tab bar on mobile (SVG icons, safe-area insets), inline top nav on desktop; no more horizontal overflow
- previews show full aspect ratio (object-fit contain) on subtle checker bg for transparency (library, studio, queue)
- 16px inputs on mobile (no iOS zoom), tactile :active feedback, larger touch targets
- keeps Klarbild identity (Space Grotesk/Mono, blue, paper, regmark), no glows/gradients

src/styles/tokens.css

@@ -56,6 +56,14 @@ a { color: var(--accent); }
 .regmark::before { left: 50%; top: 0; width: 1.5px; height: 100%; transform: translateX(-50%); }
 .regmark::after { top: 50%; left: 0; height: 1.5px; width: 100%; transform: translateY(-50%); }
 
+/* Mobile-First: 16px-Felder gegen iOS-Zoom beim Fokus */
+@media (max-width: 767px) {
+  input, select, textarea { font-size: 16px !important; }
+}
+/* Taktiles Feedback auf allen Buttons */
+button { transition: transform 0.06s ease; }
+button:active { transform: scale(0.97); }
+
 @media (prefers-reduced-motion: reduce) {
   * { animation-duration: 0.001ms !important; transition-duration: 0.001ms !important; }
 }