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/by.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 513 342"><path fill="#007C30" d="M0 0h513v342H0z"/><path fill="#CE1720" d="M0 230h513V0H0"/><path fill="#FFF" d="M100 230V0H0v342h513-413z"/><g fill="#CE1720"><path d="M28 159.6 8.6 128.2 28 97.4l19.3 30.8zM72.6 159.6l-19.3-31.4 19.3-30.8L92 128.2zM28 241.2 8.6 209.8 28 179l19.3 30.8zM72.6 241.2l-19.3-31.4L72.6 179 92 209.8z"/></g><g fill="none" stroke="#CE1720" stroke-width="7"><path d="m28 73.8-16.1-26L28 22.2l16 25.6zM72.6 73.8l-16-26 16-25.6 16.1 25.6zM28 318l-16.1-26.1L28 266.3l16 25.6zM72.6 318l-16-26.1 16-25.6 16.1 25.6z"/></g></svg>