fix: upgrade ACadSharp 3.1.32 → 3.4.9 to fix missing OBJECTS section

The DxfWriter in 3.1.32 wrote root dictionary entries referencing child
dictionary objects (ACAD_GROUP, ACAD_LAYOUT, etc.) but never serialized
the actual objects. This caused AutoCAD to report "GroupTable dictionary
was not defined in NamedObject dictionary". Version 3.4.9 includes the
root dictionary fix from PR #957.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

EtchBendLines/EtchBendLines.csproj

@@ -11,7 +11,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="ACadSharp" Version="3.1.32" />
+    <PackageReference Include="ACadSharp" Version="3.4.9" />
     <PackageReference Include="System.Configuration.ConfigurationManager" Version="8.0.0" />
   </ItemGroup>