fix(planner): distinct aria-label for export dropdown toggle

The restyled Export split-button's dropdown toggle got aria-label
"Export GPX", colliding with the main button's text and breaking the
E2E selector that clicked the old "▾" glyph. Give it a dedicated
exportOptions label (en + de) and target it in the E2E test.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

apps/planner/app/components/ExportButton.tsx

@@ -68,7 +68,7 @@ export function ExportButton({ yjs }: { yjs: YjsState }) {
         </button>
         <button
           onClick={(e) => { e.stopPropagation(); setOpen((v) => !v); }}
-          aria-label={t("exportGpx")}
+          aria-label={t("exportOptions")}
           aria-expanded={open}
           className={`${split} rounded-r-md px-2 text-text-md`}
         >