Tab Community, tombol Bayar di navbar, logo placeholder, fix crash PIN

- Bottom navbar: Home, Pesanan, Bayar (tombol tengah ke kode bayar),
  Community, Profil; menu EnakCommunity di beranda pindah ke tab
- Image placeholder: logo Enaklo diperbesar, ilustrasi gelas dihapus
- Fix assertion Navigator saat PIN gagal karena error non-PIN: flushbar
  kini tampil lewat onFailure setelah sheet PIN tertutup (bayar, tukar,
  transfer)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

lib/presentation/pages/wallet/exchange_page.dart

@@ -139,6 +139,7 @@ class _ExchangePageState extends State<ExchangePage> {
         final result = await bloc.stream.firstWhere((s) => !s.isSubmitting);
         return result.failureOption.toNullable();
       },
+      onFailure: _showFailure,
     );
 
     if (success && mounted) {
@@ -173,11 +174,6 @@ class _ExchangePageState extends State<ExchangePage> {
   Widget build(BuildContext context) {
     return MultiBlocListener(
       listeners: [
-        BlocListener<ExchangeFormBloc, ExchangeFormState>(
-          listenWhen: (p, c) => p.failureOption != c.failureOption,
-          listener: (context, state) =>
-              state.failureOption.fold(() {}, _showFailure),
-        ),
         BlocListener<ExchangeFormBloc, ExchangeFormState>(
           listenWhen: (p, c) => p.preview != c.preview && c.preview != null,
           listener: (context, state) => setState(() => _rate = state.preview),