refactor(engine): align namespaces with directory layout under OpenNest.Engine

All 132 OpenNest.Engine source files now declare namespaces matching
their nested directories: Jobs/, Jobs/Placement/, Jobs/Adapters/,
Fill/, RectanglePacking/, CirclePacking/, and engine-root types moved
from 'OpenNest' to 'OpenNest.Engine'. RootNamespace updated accordingly.
Consumers (Api, Console, Mcp, Benchmark, Training, desktop app, tests)
gained the explicit usings the move requires; CLAUDE.md updated.

OpenNest.Tests/Engine/EngineOverlapTests.cs

@@ -2,6 +2,7 @@ using OpenNest.Converters;
 using OpenNest.Geometry;
 using OpenNest.IO;
 using Xunit.Abstractions;
+using OpenNest.Engine;
 
 namespace OpenNest.Tests.Engine;
 

OpenNest.Tests/Engine/EngineRefactorSmokeTests.cs

@@ -1,4 +1,5 @@
 using OpenNest.Geometry;
+using OpenNest.Engine;
 
 namespace OpenNest.Tests.Engine;
 

OpenNest.Tests/Engine/MultiPlateNesterTests.cs

@@ -7,6 +7,7 @@ using OpenNest.Geometry;
 using OpenNest.IO;
 using Xunit;
 using Xunit.Abstractions;
+using OpenNest.Engine;
 
 namespace OpenNest.Tests.Engine;
 

OpenNest.Tests/Engine/NestPhaseExtensionsTests.cs

@@ -1,3 +1,4 @@
+using OpenNest.Engine;
 namespace OpenNest.Tests.Engine;
 
 public class NestPhaseExtensionsTests

OpenNest.Tests/Engine/NestProgressTests.cs

@@ -1,4 +1,5 @@
 using OpenNest.Geometry;
+using OpenNest.Engine;
 
 namespace OpenNest.Tests.Engine;
 

OpenNest.Tests/Engine/PlateOptimizerTests.cs

@@ -1,4 +1,5 @@
 using OpenNest.Geometry;
+using OpenNest.Engine;
 
 namespace OpenNest.Tests.Engine;