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/pk.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 900 600"><path fill="#FFF" d="M0 0h900v600H0z"/><path fill="#01411C" d="M225 0h675v600H225z"/><path fill="#FFF" d="M562.5 120c99.4 0 180 80.6 180 180s-80.6 180-180 180-180-80.6-180-180 80.6-180 180-180z"/><path fill="#01411C" d="M498.9 135.8c68.1-60.5 172.4-54.4 232.9 13.7s54.4 172.4-13.7 232.9-172.4 54.4-232.9-13.7-54.4-172.4 13.7-232.9z"/><path fill="#FFF" d="m628.1 165.3 75.8 85.3-111.5-24.4L697 180.4l-57.7 98.5-11.2-113.6z"/></svg>