fix: a calendar date is the same day everywhere; legal pages use the shared language picker

formatDate read a date-only value as UTC midnight and showed it in the viewer's zone, so the legal pages' last update read a day early west of UTC. Date-only values are shown in UTC. The legal pages' hand-rolled language buttons are the landing page's LanguageSwitcher. formatDateTime and formatDate get the two-language test formatNumber already had.

frontend/src/components/legal/LegalLayout.tsx

@@ -9,9 +9,10 @@
 import { useEffect, useState, type ReactNode } from "react";
 import { useTranslation } from "react-i18next";
 
-import { LANGUAGES, setLanguage } from "../../i18n";
+import { setLanguage, type LangCode } from "../../i18n";
 import { formatDate } from "../../lib/format";
 import { send } from "../../lib/http";
+import LanguageSwitcher from "../LanguageSwitcher";
 
 // The day the text last changed materially — bump it with every edit of either body.
 const LAST_UPDATED = "2026-09-17";
@@ -77,20 +78,8 @@ export default function LegalLayout({ title, children }: { title: string; childr
           <a href="/" className="inline-block text-2xl font-bold tracking-tight">
             Sift<span className="text-accent">lode</span>
           </a>
-          <div role="group" aria-label={t("legal.languageLabel")} className="flex gap-1 text-xs">
-            {LANGUAGES.map((lang) => (
-              <button
-                key={lang.code}
-                type="button"
-                lang={lang.code}
-                aria-pressed={i18n.language?.startsWith(lang.code) ?? false}
-                onClick={() => setLanguage(lang.code)}
-                className="rounded-md px-2 py-1 text-muted hover:text-fg aria-pressed:bg-card aria-pressed:text-fg"
-              >
-                {lang.label}
-              </button>
-            ))}
-          </div>
+          {/* The landing page's own picker, so the public pages switch language one way. */}
+          <LanguageSwitcher value={i18n.language as LangCode} onChange={setLanguage} />
         </div>
         <div className="glass rounded-2xl p-8">
           <h1 className="text-2xl font-semibold">{title}</h1>