feat: Add refresh token endpoint and remember me support

- Add POST /auth/refresh endpoint for token renewal
- Only set refresh token cookie when rememberMe is true
- Add rememberMe field to login validator schema

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/routes/auth.routes.js

@@ -25,6 +25,9 @@ router.post(
   authController.login
 );
 
+// Refresh access token (public - uses refresh token from cookie)
+router.post('/refresh', authController.refreshToken);
+
 /**
  * Protected routes (vyžadujú autentifikáciu)
  */