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/validators/auth.validators.js

@@ -15,6 +15,7 @@ export const loginSchema = z.object({
       invalid_type_error: 'Heslo musí byť text',
     })
     .min(1, 'Heslo nemôže byť prázdne'),
+  rememberMe: z.boolean().optional().default(false),
 });
 
 // Set new password schema (krok 2)