feat(core,io): persist nest status and made-by in nest files

Add NestStatus (Quote/ToBeCut/HasBeenCut) plus MadeBy on Nest, written as
additive camelCase nest.json fields with PascalCase enum strings matching
the units convention. Legacy files and unknown status values fall back to
Quote. The nest info dialog gains a Status dropdown and Made By box.

OpenNest.Core/NestStatus.cs

@@ -0,0 +1,13 @@
+namespace OpenNest
+{
+    /// <summary>
+    /// Shop-floor workflow state of a saved nest, persisted as a string in
+    /// <c>nest.json</c> so unknown future values can fall back safely.
+    /// </summary>
+    public enum NestStatus
+    {
+        Quote,
+        ToBeCut,
+        HasBeenCut,
+    }
+}