feat: Settings page — profile + link/unlink providers via SuperOAuth API

- Store SuperOAuth access_token in localStorage for profile API calls
- Settings page: profile info, linked providers, link/unlink buttons
- Navbar: settings icon replaces logout button

Frontend/src/components/navbar.jsx

@@ -76,9 +76,9 @@ export default function Navbar({ navData, toggleRain, setToggleRain }) {
         {user ? (
           <div className="auth-nav">
             <span className="auth-nickname">{user.nickname}</span>
-            <button className="auth-btn" onClick={logout} type="button">
-              Déconnexion
-            </button>
+            <Link className="mainLink" to="/settings" title="Paramètres">
+              ⚙
+            </Link>
           </div>
         ) : (
           <Link className="mainLink" to="/login">