add placeholder inbox page

lib/pages/inbox.dart

@@ -0,0 +1,22 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_hooks/flutter_hooks.dart';
+
+class InboxPage extends HookWidget {
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(),
+      body: Center(
+        child: Column(
+          mainAxisAlignment: MainAxisAlignment.center,
+          children: [
+            Text(
+              '🚧 WORK IN PROGRESS 🚧',
+              style: Theme.of(context).textTheme.headline5,
+            )
+          ],
+        ),
+      ),
+    );
+  }
+}