docs: update README with accurate features and add roadmap

Remove NFP pair fitting claim from features (not yet integrated).
Qualify lead-in/lead-out as engine-only (UI coming soon).
Mark --autonest CLI option as experimental. Add Roadmap section
with planned work: NFP nesting, lead-in UI, sheet cut-offs,
post-processors, and shape library UI.

Add documentation maintenance instruction to CLAUDE.md requiring
README.md and CLAUDE.md updates when project structure changes.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

OpenNest.Engine/Nfp/INestOptimizer.cs

@@ -0,0 +1,38 @@
+using System.Collections.Generic;
+using System.Threading;
+using OpenNest.Geometry;
+
+namespace OpenNest
+{
+    /// <summary>
+    /// Result of a nest optimization run.
+    /// </summary>
+    public class NestResult
+    {
+        /// <summary>
+        /// The best sequence found: (drawingId, rotation, drawing) tuples in placement order.
+        /// </summary>
+        public List<(int drawingId, double rotation, Drawing drawing)> Sequence { get; set; }
+
+        /// <summary>
+        /// The score achieved by the best sequence.
+        /// </summary>
+        public FillScore Score { get; set; }
+
+        /// <summary>
+        /// Number of iterations performed.
+        /// </summary>
+        public int Iterations { get; set; }
+    }
+
+    /// <summary>
+    /// Interface for nest optimization algorithms that search for the best
+    /// part ordering and rotation to maximize plate utilization.
+    /// </summary>
+    public interface INestOptimizer
+    {
+        NestResult Optimize(List<NestItem> items, Box workArea, NfpCache cache,
+            Dictionary<int, List<double>> candidateRotations,
+            CancellationToken cancellation = default);
+    }
+}