fix(ux): prevent iOS auto-zoom on inputs + lazy-load page CSS

Increase font-size to 16px on mobile for shopping quick-add inputs,
notes search, and contacts search. Desktop breakpoint restores compact
sizes. Move 9 page-specific stylesheets from index.html to on-demand
loading in router.js, reducing initial CSS payload.

public/styles/contacts.css

@@ -61,7 +61,7 @@
   border: 1.5px solid var(--color-border);
   background-color: var(--color-surface-2);
   color: var(--color-text-primary);
-  font-size: var(--text-sm);
+  font-size: var(--text-md);
   transition: border-color var(--transition-fast);
   min-height: 36px;
 }
@@ -72,6 +72,10 @@
   background-color: var(--color-surface);
 }
 
+@media (min-width: 1024px) {
+  .contacts-toolbar__search-input { font-size: var(--text-sm); }
+}
+
 /* --------------------------------------------------------
  * Kategorie-Filter (horizontal scroll)
  * -------------------------------------------------------- */