feat: language picker with flags, paging and follow mode, translation run in the floating window

Language picker with search and SVG flags, real pagination with locate, one global machine translation run shown next to uploads.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

frontend/public/flags/mn.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 513 342"><path fill="#0066b2" d="M0 0h513v342H0z"/><g fill="#da2031"><path d="M342 0h171v342H342zM0 0h171v342H0z"/></g><g fill="#ffd300"><path d="M108.3 166.3h14.8v74.2h-14.8zM48.9 166.3h14.8v74.2H48.9z"/><circle cx="86" cy="203.4" r="14.8"/><path d="M71.2 225.7h29.7v14.8H71.2zM71.2 166.3h29.7v14.8H71.2z"/><circle cx="86" cy="144" r="14.8"/><path d="M76.3 123.9h19.5L86 108.3z"/></g></svg>