feat(nav): add header navigation and show Steam ID on dashboard

Header links to Dashboard, Library and Settings. The logo, the login page and
the landing page lead logged-in users to the dashboard. Expired tokens are
removed, and a 403 on the dashboard logs out. Remove the dev dummy token.

src/pages/Dashboard.jsx

@@ -56,7 +56,7 @@ const Dashboard = () => {
                     if (data.steamId) {
                         await fetchSteamCount();
                     }
-                } else if (profileResponse.status === 401) {
+                } else if (profileResponse.status === 401 || profileResponse.status === 403) {
                     localStorage.removeItem('tbp_jwt');
                     navigate('/login');
                 } else {
@@ -107,6 +107,17 @@ const Dashboard = () => {
                     <p className="text-lg text-slate-600 dark:text-slate-300">
                         {userData?.dashboardMessage}
                     </p>
+                    {userData?.steamId ? (
+                        <p className="mt-2 text-sm text-slate-500 dark:text-slate-400">
+                            <i className="mdi mdi-steam mr-1"></i>
+                            {t('SETTINGS.STEAM_ID')}: <span className="font-mono">{userData.steamId}</span>
+                        </p>
+                    ) : (
+                        <Link to="/settings" className="mt-2 inline-block text-sm text-blue-600 dark:text-blue-400 hover:underline">
+                            <i className="mdi mdi-steam mr-1"></i>
+                            {t('DASHBOARD.NO_STEAM_ID')}
+                        </Link>
+                    )}
                     {userData?.steamId && (
                         <div className="mt-4">
                             <SyncStatusBadge

src/pages/LandingPage.jsx

@@ -1,5 +1,6 @@
 import {useTranslation} from 'react-i18next';
 import {Link} from 'react-router-dom';
+import {getValidToken} from '../utils/auth.js';
 import StatCard from '../components/StatCard.jsx';
 
 import usePublicStats from '../hooks/usePublicStats.js';
@@ -25,9 +26,15 @@ export default function LandingPage() {
                 <p className="text-lg text-slate-600 dark:text-slate-400 max-w-2xl mx-auto mb-8">
                     {t('MAIN.DESCRIPTION')}
                 </p>
-                <Link to="/login" className="bg-blue-600 hover:bg-blue-500 text-white px-8 py-3 rounded-xl font-bold text-lg transition-all shadow-lg shadow-blue-500/30">
-                    {t('MAIN.GET_STARTED')}
-                </Link>
+                {getValidToken() ? (
+                    <Link to="/dashboard" className="bg-blue-600 hover:bg-blue-500 text-white px-8 py-3 rounded-xl font-bold text-lg transition-all shadow-lg shadow-blue-500/30">
+                        {t('NAV.TO_DASHBOARD')}
+                    </Link>
+                ) : (
+                    <Link to="/login" className="bg-blue-600 hover:bg-blue-500 text-white px-8 py-3 rounded-xl font-bold text-lg transition-all shadow-lg shadow-blue-500/30">
+                        {t('MAIN.GET_STARTED')}
+                    </Link>
+                )}
             </section>
 
             <section className="w-full max-w-5xl mb-16">

src/pages/LoginPage.jsx

@@ -1,6 +1,7 @@
 import {useTranslation} from 'react-i18next';
 import {useState} from 'react';
-import {Link, useNavigate} from 'react-router-dom';
+import {Link, Navigate, useNavigate} from 'react-router-dom';
+import {getValidToken} from '../utils/auth.js';
 
 export default function LoginPage() {
     const {t} = useTranslation();
@@ -38,10 +39,7 @@ export default function LoginPage() {
             if (response.ok) {
                 // HTTP 200 OK
                 localStorage.setItem('tbp_jwt', data.token);
-                setFeedback({message: 'Login successful!', isError: false});
-                setTimeout(() => {
-                    navigate('/dashboard');
-                }, 500);
+                navigate('/dashboard', {replace: true});
             } else {
                 // HTTP 401 Unauthorized or other errors
                 setFeedback({
@@ -61,6 +59,10 @@ export default function LoginPage() {
         }
     };
 
+    if (getValidToken()) {
+        return <Navigate to="/dashboard" replace/>;
+    }
+
     return (
         <div className="flex min-h-screen items-center justify-center bg-slate-50 dark:bg-slate-900 px-4">
             <div className="w-full max-w-md bg-white dark:bg-slate-800 rounded-xl shadow-lg p-8">