start adding login flow

lib/widgets/appbar.dart

@@ -0,0 +1,35 @@
+import "dart:io";
+import "package:flutter/material.dart";
+
+class Appbar extends StatelessWidget implements PreferredSizeWidget {
+  final Widget? leading;
+  final Widget? title;
+  final Color? backgroundColor;
+  final double? scrolledUnderElevation;
+  final List<Widget> actions;
+  const Appbar({
+    super.key,
+    this.title,
+    this.backgroundColor,
+    this.scrolledUnderElevation,
+    this.leading,
+    this.actions = const [],
+  });
+
+  @override
+  Size get preferredSize => AppBar().preferredSize;
+
+  @override
+  AppBar build(BuildContext context) => AppBar(
+    leading: leading,
+    backgroundColor: backgroundColor,
+    scrolledUnderElevation: scrolledUnderElevation,
+    actionsPadding: EdgeInsets.symmetric(horizontal: 8),
+    title: title,
+    actions: [
+      ...actions,
+      if (!(Platform.isAndroid || Platform.isIOS))
+        IconButton(onPressed: () => exit(0), icon: Icon(Icons.close)),
+    ],
+  );
+}