chore: remove unused NFP nesting code

Delete OpenNest.Engine/Nfp (AutoNester, BottomLeftFill, NfpCache,
SimulatedAnnealing, INestOptimizer, PlacedPart, SequenceEntry), the Core
InnerFitPolygon, and the NestPhase.Nfp member. None had callers outside the
folder: console --autonest and MCP autonest_plate call engine.Nest(), not
AutoNester.

Drop the Nfp cases from NestPhaseExtensionsTests, fix the --autonest help
text, and update CLAUDE.md. NoFitPolygon stays; BestFit pair evaluation
still uses it.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

OpenNest.Console/Program.cs

@@ -597,7 +597,7 @@ static class NestConsole
             "  --template <path>      Nest template for plate defaults (thickness, quadrant, material, spacing)"
         );
         Console.Error.WriteLine(
-            "  --autonest             Use NFP-based mixed-part autonesting instead of linear fill"
+            "  --autonest             Use mixed-part autonesting (engine Nest) instead of linear fill"
         );
         Console.Error.WriteLine(
             "  --keep-parts           Don't clear existing parts before filling"