Flutter: tampilkan URL server tersimpan saat layar login berikutnya

- Session.clear() kini hapus sesi (user/pass) tapi sisakan URL terakhir
- + Session.readLastUrl()
- LoginScreen mengisi field URL dari URL terakhir saat dibuka
- sesudah logout login lagi URL sudah terisi, tak perlu ketik ulang

flutter/lib/main.dart

@@ -96,6 +96,19 @@ class _LoginScreenState extends State<LoginScreen> {
   bool _busy = false;
   String? _error;
 
+  @override
+  void initState() {
+    super.initState();
+    _loadUrl();
+  }
+
+  Future<void> _loadUrl() async {
+    final url = await Session.readLastUrl();
+    if (url != null && mounted) {
+      setState(() => _url.text = url);
+    }
+  }
+
   @override
   Widget build(BuildContext context) {
     return Scaffold(