feat(ui): add ActiveColorScheme user setting

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

OpenNest/Properties/Settings.Designer.cs

@@ -226,5 +226,17 @@ namespace OpenNest.Properties {
                 this["CuttingParametersJson"] = value;
             }
         }
+
+        [global::System.Configuration.UserScopedSettingAttribute()]
+        [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]
+        [global::System.Configuration.DefaultSettingValueAttribute("Classic")]
+        public string ActiveColorScheme {
+            get {
+                return ((string)(this["ActiveColorScheme"]));
+            }
+            set {
+                this["ActiveColorScheme"] = value;
+            }
+        }
     }
 }

OpenNest/Properties/Settings.settings

@@ -53,5 +53,8 @@
     <Setting Name="CuttingParametersJson" Type="System.String" Scope="User">
       <Value Profile="(Default)" />
     </Setting>
+    <Setting Name="ActiveColorScheme" Type="System.String" Scope="User">
+      <Value Profile="(Default)">Classic</Value>
+    </Setting>
   </Settings>
 </SettingsFile>