fix(auth): redirect active sessions from /login

/api/auth/status did not expose whether the auth cookie corresponds to a
valid dashboard session, so /login could only detect "auth disabled"
(requireLogin === false) and not "already logged in". Add authenticated
to the status response and redirect from /login when it's true.

src/app/login/page.js

@@ -37,7 +37,7 @@ export default function LoginPage() {
 
         if (res.ok) {
           const data = await res.json();
-          if (data.requireLogin === false) {
+          if (data.authenticated === true || data.requireLogin === false) {
             window.location.assign("/dashboard");
             return;
           }