refactor(engine): extract AutoNester and reorganize NestEngine

Move NFP-based AutoNest logic (polygon extraction, rotation computation,
simulated annealing) into dedicated AutoNester class. Consolidate duplicate
FillWithPairs overloads, extract BuildCandidateAngles and BuildProgressSummary,
reorganize NestEngine into logical sections. Update callers in Console,
MCP tools, and MainForm to use AutoNester.Nest.

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

OpenNest.Mcp/Tools/NestingTools.cs

@@ -233,7 +233,7 @@ namespace OpenNest.Mcp.Tools
                 items.Add(new NestItem { Drawing = drawing, Quantity = qtys[i] });
             }
 
-            var parts = NestEngine.AutoNest(items, plate);
+            var parts = AutoNester.Nest(items, plate);
             plate.Parts.AddRange(parts);
 
             var sb = new StringBuilder();