♿️ Fix AA contrast and move mobile language selector to header row

Darken burufugu primary-600 to pass 4.5:1 on white, bump the search
shortcut hint to neutral-500, and surface the language switcher in
the visible mobile header row instead of the menu dialog.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

assets/css/main.css

@@ -486,7 +486,8 @@ body:has(#mobile-menu-toggle:checked) {
 }
 
 /* Dropdowns near the end of the bar open leftward so they stay on screen */
-.nested-menu:nth-last-child(-n + 3) .menuhide {
+.nested-menu:nth-last-child(-n + 3) .menuhide,
+.mobile-header-row .menuhide {
   inset-inline-end: 0;
 }