Add order entities and mocks for client order feature

Introduces new domain entities for order types and one-time orders, along with their positions. Adds a mock OrderRepository to the data_connect package and wires it into the module. Updates localization files for new order flows and refactors Equatable usage for consistency. Also adds a minus icon to the design system.

apps/mobile/packages/design_system/lib/src/ui_icons.dart

@@ -48,6 +48,9 @@ class UiIcons {
   /// Plus/Add icon
   static const IconData add = _IconLib.plus;
 
+  /// Minus icon
+  static const IconData minus = _IconLib.minus;
+
   /// Edit icon
   static const IconData edit = _IconLib.edit2;