feat: initial Pyramid project scaffold

lib/layout/shell_page.dart

@@ -0,0 +1,19 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:pyramid/layout/panel_layout.dart';
+
+class ShellPage extends ConsumerWidget {
+  final Widget child;
+  const ShellPage({super.key, required this.child});
+
+  @override
+  Widget build(BuildContext context, WidgetRef ref) {
+    final isWide = MediaQuery.sizeOf(context).width >= 700;
+
+    return Scaffold(
+      body: isWide
+          ? PanelLayout(mainContent: child)
+          : child,
+    );
+  }
+}