Add app source and tests

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

lib/Peach/designs/Responsive.dart

@@ -0,0 +1,58 @@
+import 'package:flutter/material.dart';
+
+import '../about/internal/application/TextType.dart';
+import 'text/Text.dart';
+
+/// Picks one of three layouts for the current width. Screens are built as
+/// `_mobileView` / `_tabletView` / `_desktopView` methods on their State and
+/// handed to this widget, rather than as one layout littered with width checks.
+class Responsive extends StatelessWidget {
+  final Widget mobile;
+  final Widget tablet;
+  final Widget desktop;
+
+  const Responsive({
+    super.key,
+    required this.desktop,
+    required this.mobile,
+    required this.tablet,
+  });
+
+  /// mobile < 650
+  static bool isMobile(BuildContext context) =>
+      MediaQuery.sizeOf(context).width < 650;
+
+  /// tablet >= 650
+  static bool isTablet(BuildContext context) =>
+      MediaQuery.sizeOf(context).width >= 650;
+
+  /// desktop >= 1100
+  static bool isDesktop(BuildContext context) =>
+      MediaQuery.sizeOf(context).width >= 1100;
+
+  @override
+  Widget build(BuildContext context) {
+    return LayoutBuilder(
+      builder: (context, constraints) {
+        if (isDesktop(context)) {
+          return desktop;
+        } else if (isTablet(context)) {
+          return tablet;
+        } else if (isMobile(context)) {
+          return mobile;
+        } else {
+          return SizedBox(
+            width: double.infinity,
+            height: double.infinity,
+            child: Column(
+              mainAxisSize: MainAxisSize.max,
+              crossAxisAlignment: CrossAxisAlignment.center,
+              mainAxisAlignment: MainAxisAlignment.center,
+              children: [text("NOT SUPPORTED", 12, TextType.Bold)],
+            ),
+          );
+        }
+      },
+    );
+  }
+}