Add multilingual support, competition close/reopen, and backup directory

web/login.js

@@ -1,6 +1,8 @@
 (async function () {
   const root = document.getElementById("app");
 
+  await setLang(detectInitialLang());
+
   // If already signed in, skip the login form.
   try {
     const u = await API.me();
@@ -17,7 +19,7 @@
     const passwordInput = el("input", { type: "password", autocomplete: "current-password", placeholder: t("password") });
     const errorBox = el("div", { class: "muted", style: { color: "var(--danger)", display: "none" } });
     const langSelect = el("select",
-      { onchange: (e) => { setLang(e.target.value); render(); } },
+      { onchange: async (e) => { await setLang(e.target.value); render(); } },
       ...I18N_AVAILABLE.map((l) => el("option", { value: l, selected: l === CURRENT_LANG }, I18N_NAMES[l]))
     );