feat: add Shape Library UI with configurable shapes and flange presets

Add a Shape Library dialog (Nest > Shape Library) for creating drawings
from built-in parametric shapes. Supports configuration presets loaded
from JSON files — ships with 136 standard pipe flanges. Parameters use
TextBox inputs with architectural unit parsing (feet/inches, fractions).

- ShapeLibraryForm with split layout: shape list, preview, parameters
- ShapePreviewControl for auto-zoom rendering with info overlay
- ArchUnits utility for parsing architectural measurements
- SetPreviewDefaults() on all ShapeDefinition subclasses
- Convention-based config discovery (Configurations/{ShapeName}.json)

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

OpenNest/OpenNest.csproj

@@ -10,6 +10,11 @@
   <ItemGroup>
     <Compile Remove="Controls\LayoutViewGL.cs" />
   </ItemGroup>
+  <ItemGroup>
+    <Content Include="Configurations\**\*.json">
+      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+    </Content>
+  </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="..\OpenNest.Api\OpenNest.Api.csproj" />
     <ProjectReference Include="..\OpenNest.Core\OpenNest.Core.csproj" />