test(web): reset i18n to English after the language-switch test

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

web/src/i18n/i18n.test.tsx

@@ -1,4 +1,4 @@
-import { expect, test, beforeEach } from "vitest";
+import { expect, test, beforeEach, afterEach } from "vitest";
 import { render, screen, act } from "@testing-library/react";
 import { useTranslation } from "react-i18next";
 import i18n from "./index";
@@ -8,6 +8,12 @@ beforeEach(async () => {
   await i18n.changeLanguage("en");
 });
 
+// Leave the shared i18n singleton on English so language-dependent assertions in
+// other test files are never affected by this file's runtime switch to Swedish.
+afterEach(async () => {
+  await i18n.changeLanguage("en");
+});
+
 function Probe() {
   const { t } = useTranslation();
   const { setLocale } = useLocale();