feat: responsive layout.

app/lib/constants/constants.dart

@@ -0,0 +1,18 @@
+import 'package:flutter/cupertino.dart';
+
+const double localManagerPanelWidth = 200;
+
+const double marketPanelWidth = 200;
+
+const shortDuration = const Duration(milliseconds: 100);
+
+const mediumDuration = const Duration(milliseconds: 300);
+
+const longDuration = const Duration(milliseconds: 500);
+
+const minWindowSize = const Size(800, 600);
+
+enum PanelType {
+  local_manager,
+  market,
+}