chore: upgrade Nullean.Argh to 0.12.0

Fixes:
- PR #28: DTO XML summaries now render in --help; global options show short
  flag first (e.g. -l, --log-level)
- PR #29: enum choices listed lowercase in help (html, elasticsearch, ...)
- PR #30: [Existing] on optional nullable FileInfo?/DirectoryInfo? no longer
  throws ArgumentNullException when the flag is omitted
- PR #31: MapAndRootAlias root help and leading flag handling fixed

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

Author: Mpdreamz

Directory.Packages.props

@@ -69,9 +69,9 @@
     <PackageVersion Include="FSharp.Core" Version="10.1.201" />
   </ItemGroup>
   <ItemGroup>
-    <PackageVersion Include="Nullean.Argh" Version="0.11.0" />
-    <PackageVersion Include="Nullean.Argh.Hosting" Version="0.11.0" />
-    <PackageVersion Include="Nullean.Argh.Interfaces" Version="0.11.0" />
+    <PackageVersion Include="Nullean.Argh" Version="0.12.0" />
+    <PackageVersion Include="Nullean.Argh.Hosting" Version="0.12.0" />
+    <PackageVersion Include="Nullean.Argh.Interfaces" Version="0.12.0" />
     <PackageVersion Include="Crayon" Version="2.0.69" />
     <PackageVersion Include="DotNet.Glob" Version="3.1.3" />
     <PackageVersion Include="Errata" Version="0.16.0" />
@@ -88,7 +88,7 @@
     <PackageVersion Include="Proc" Version="0.13.0" />
     <PackageVersion Include="RazorSlices" Version="0.9.5" />
     <PackageVersion Include="Samboy063.Tomlet" Version="6.0.0" />
-    <PackageVersion Include="Sep" Version="0.11.0" />
+    <PackageVersion Include="Sep" Version="0.12.0" />
     <PackageVersion Include="Slugify.Core" Version="4.0.1" />
     <PackageVersion Include="SoftCircuits.IniFileParser" Version="2.7.0" />
     <PackageVersion Include="System.IO.Abstractions" Version="22.1.1" />