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/Fill/BestCombination.cs

@@ -0,0 +1,81 @@
+using System;
+using OpenNest.Math;
+
+namespace OpenNest
+{
+    internal static class BestCombination
+    {
+        public static bool FindFrom2(double length1, double length2, double overallLength, out int count1, out int count2)
+        {
+            overallLength += Tolerance.Epsilon;
+
+            if (length1 > overallLength)
+            {
+                if (length2 > overallLength)
+                {
+                    count1 = 0;
+                    count2 = 0;
+                    return false;
+                }
+
+                count1 = 0;
+                count2 = (int)System.Math.Floor(overallLength / length2);
+                return true;
+            }
+
+            if (length2 > overallLength)
+            {
+                count1 = (int)System.Math.Floor(overallLength / length1);
+                count2 = 0;
+                return true;
+            }
+
+            var maxCountLength1 = (int)System.Math.Floor(overallLength / length1);
+
+            count1 = maxCountLength1;
+            count2 = 0;
+
+            var remnant = overallLength - maxCountLength1 * length1;
+
+            if (remnant.IsEqualTo(0))
+                return true;
+
+            for (int countLength1 = 0; countLength1 <= maxCountLength1; ++countLength1)
+            {
+                var remnant1 = overallLength - countLength1 * length1;
+
+                if (remnant1 >= length2)
+                {
+                    var countLength2 = (int)System.Math.Floor(remnant1 / length2);
+                    var remnant2 = remnant1 - length2 * countLength2;
+
+                    if (!(remnant2 < remnant))
+                        continue;
+
+                    count1 = countLength1;
+                    count2 = countLength2;
+
+                    if (remnant2.IsEqualTo(0))
+                        break;
+
+                    remnant = remnant2;
+                }
+                else
+                {
+                    if (!(remnant1 < remnant))
+                        continue;
+
+                    count1 = countLength1;
+                    count2 = 0;
+
+                    if (remnant1.IsEqualTo(0))
+                        break;
+
+                    remnant = remnant1;
+                }
+            }
+
+            return true;
+        }
+    }
+}