feat(web): i18n with react-i18next — Albanian default, English second

Add react-i18next with two key-parity-checked catalogs (sq default/fallback, en).
Active language driven by the logged-in user's stored preference (applied after
/me resolves); SQ/EN toggle in the header persists via PUT /api/auth/language.
Translate the booth (screen, pay/exit modal, active sessions, snapshots, status),
Login, ShiftControl, SiteSettings, PermitManager, TariffComposer.

SetupWizard deferred (its content is server-provided; needs backend catalog i18n).

apps/web/src/lib/i18n/index.ts

@@ -0,0 +1,33 @@
+import i18n from "i18next";
+import { initReactI18next } from "react-i18next";
+import { sq } from "./sq.js";
+import { en } from "./en.js";
+
+// i18next setup for the operator UI. Albanian (sq) is the DEFAULT and the fallback;
+// English (en) is the second language. The active language is the LOGGED-IN USER's
+// stored preference (users.language), applied via setLanguage() after auth resolves
+// — not localStorage, not the browser. Printed tickets are NOT governed by this
+// (always Albanian, customer-facing). See wiki/concepts/i18n.md.
+
+export type Lang = "sq" | "en";
+
+// Single flat namespace; keys are dot-paths (e.g. "booth.processTicket"). Nested
+// objects in the catalogs are walked by i18next's keySeparator.
+void i18n.use(initReactI18next).init({
+  resources: {
+    sq: { translation: sq },
+    en: { translation: en },
+  },
+  lng: "sq",
+  fallbackLng: "sq",
+  interpolation: { escapeValue: false }, // React already escapes
+  returnNull: false,
+});
+
+/** Apply a language (e.g. after login resolves the user's preference). No-op if
+ *  already active. */
+export function setLanguage(lang: Lang): void {
+  if (i18n.language !== lang) void i18n.changeLanguage(lang);
+}
+
+export default i18n;