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/main/widgets/bottom_navbar.dart

@@ -1,16 +1,33 @@
 import 'package:auto_route/auto_route.dart';
 import 'package:flutter/material.dart';
 
+import '../../../../common/theme/theme.dart';
+
 class MainBottomNavbar extends StatelessWidget {
   final TabsRouter tabsRouter;
-  const MainBottomNavbar({super.key, required this.tabsRouter});
+  final VoidCallback onPayTap;
+  const MainBottomNavbar({
+    super.key,
+    required this.tabsRouter,
+    required this.onPayTap,
+  });
+
+  /// Slot tengah hanya tempat label tombol Bayar; lingkarannya
+  /// [MainPayButton] yang menempel di atas navbar.
+  static const int _payIndex = 2;
 
   @override
   Widget build(BuildContext context) {
+    final activeIndex = tabsRouter.activeIndex;
+
     return BottomNavigationBar(
-      currentIndex: tabsRouter.activeIndex,
+      currentIndex: activeIndex >= _payIndex ? activeIndex + 1 : activeIndex,
       onTap: (index) {
-        tabsRouter.setActiveIndex(index);
+        if (index == _payIndex) {
+          onPayTap();
+          return;
+        }
+        tabsRouter.setActiveIndex(index > _payIndex ? index - 1 : index);
       },
       items: const [
         BottomNavigationBarItem(
@@ -28,6 +45,16 @@ class MainBottomNavbar extends StatelessWidget {
           label: 'Pesanan',
           tooltip: 'Pesanan',
         ),
+        BottomNavigationBarItem(
+          icon: SizedBox(height: 24),
+          label: 'Bayar',
+          tooltip: 'Bayar di kasir',
+        ),
+        BottomNavigationBarItem(
+          icon: Icon(Icons.groups),
+          label: 'Community',
+          tooltip: 'Community',
+        ),
         BottomNavigationBarItem(
           icon: Icon(Icons.person),
           label: 'Profil',
@@ -37,3 +64,40 @@ class MainBottomNavbar extends StatelessWidget {
     );
   }
 }
+
+/// Seperti [FloatingActionButtonLocation.centerDocked], tapi tombolnya lebih
+/// menonjol ke atas supaya tidak menempel ke label "Bayar".
+class MainPayButtonLocation extends StandardFabLocation
+    with FabCenterOffsetX, FabDockedOffsetY {
+  const MainPayButtonLocation();
+
+  static const double _raise = 10;
+
+  @override
+  double getOffsetY(
+    ScaffoldPrelayoutGeometry scaffoldGeometry,
+    double adjustment,
+  ) => super.getOffsetY(scaffoldGeometry, adjustment) - _raise;
+}
+
+/// Tombol bulat di tengah navbar, dipasang di [MainPayButtonLocation].
+class MainPayButton extends StatelessWidget {
+  final VoidCallback onPressed;
+  const MainPayButton({super.key, required this.onPressed});
+
+  @override
+  Widget build(BuildContext context) {
+    return FloatingActionButton(
+      onPressed: onPressed,
+      // Halaman tab (mis. Community) juga punya FAB; tanpa hero supaya tag
+      // default tidak bentrok saat pindah halaman.
+      heroTag: null,
+      tooltip: 'Bayar di kasir',
+      elevation: 4,
+      backgroundColor: AppColor.primary,
+      foregroundColor: AppColor.white,
+      shape: const CircleBorder(),
+      child: const Icon(Icons.qr_code_scanner_rounded, size: 28),
+    );
+  }
+}