feat(profile): set a display name and greet with it on the dashboard

Settings: new Profil card with display name and Steam ID. Registration: optional display name. The dashboard falls back to the email prefix when no display name is set.

src/pages/Dashboard.jsx

@@ -127,7 +127,7 @@ const Dashboard = () => {
                 <div className="relative min-w-0">
                     <p className="text-sm font-medium text-muted-foreground">{t('DASHBOARD.WELCOME_BACK')}</p>
                     <h1 className="mt-1 text-3xl md:text-4xl font-bold tracking-tight truncate">
-                        {t('DASHBOARD.HELLO')} {userData?.email?.split('@')[0]} 👋
+                        {t('DASHBOARD.HELLO')} {userData?.displayName ?? userData?.email?.split('@')[0]} 👋
                     </h1>
                     {hasSteamId ? (
                         <Badge variant="outline" className="mt-3 gap-1.5 font-mono text-muted-foreground">