fix(auth): redirect already-signed-in users away from the register page

Mirrors the login guard: visiting /register while authenticated redirects to the
dashboard home (/) instead of showing the form. Gated on _hasHydrated; shows a
brief redirecting state. Reuses the existing auth.redirecting string.

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

web/dashboard/src/app/[locale]/register/page.tsx

@@ -58,8 +58,17 @@ function RegisterForm() {
   const t = useTranslations("auth");
   const router = useRouter();
   const setAuth = useAuthStore((s) => s.setAuth);
+  const user = useAuthStore((s) => s.user);
+  const hasHydrated = useAuthStore((s) => s._hasHydrated);
   const searchParams = useSearchParams();
 
+  // Already signed in? Don't show the register form — send them into the app.
+  // Gate on _hasHydrated so a not-yet-rehydrated (null) session isn't misread.
+  const alreadyAuthed = hasHydrated && !!user?.accessToken;
+  useEffect(() => {
+    if (alreadyAuthed) router.replace("/");
+  }, [alreadyAuthed, router]);
+
   const [phone, setPhone] = useState(searchParams.get("phone") ?? "");
   const [cafeName, setCafeName] = useState("");
   const [slug, setSlug] = useState("");
@@ -123,6 +132,14 @@ function RegisterForm() {
     }
   };
 
+  if (alreadyAuthed) {
+    return (
+      <div className="flex min-h-screen items-center justify-center bg-muted/30 p-4">
+        <p className="text-sm text-muted-foreground">{t("redirecting")}</p>
+      </div>
+    );
+  }
+
   return (
     <div className="flex min-h-screen items-center justify-center bg-muted/30 p-4">
       <Card className="w-full max-w-md">