Fix CI pack errors: remove duplicate license/readme metadata

- Remove PackageReadmeFile from Directory.Build.props (was causing NU5039
  on Domain and Abstractions which don't include a readme in their pack)
- Remove PackageLicenseFile from LibEmiddle.csproj (was causing NU5033 —
  cannot specify both PackageLicenseExpression and PackageLicenseFile)
- Bump VersionPrefix in Directory.Build.props to 2.6.0

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

Author: rbenzing

Directory.Build.props

@@ -5,14 +5,13 @@
     <Copyright>Copyright © $(Company) $([System.DateTime]::Now.Year)</Copyright>
     <Authors>Russell Benzing</Authors>
     <Company>Russell Benzing Inc</Company>
-    <VersionPrefix>2.5.0</VersionPrefix>
+    <VersionPrefix>2.6.0</VersionPrefix>
     <VersionSuffix></VersionSuffix>
     <PackageLicenseExpression>MIT</PackageLicenseExpression>
     <PackageProjectUrl>https://github.com/rbenzing/LibEmiddle</PackageProjectUrl>
     <RepositoryUrl>https://github.com/rbenzing/LibEmiddle.git</RepositoryUrl>
     <RepositoryType>git</RepositoryType>
     <PackageTags>encryption;e2ee;security;cryptography;libsodium</PackageTags>
-    <PackageReadmeFile>README.md</PackageReadmeFile>
   </PropertyGroup>
 
   <!-- Common build settings -->

LibEmiddle/LibEmiddle.csproj

@@ -19,7 +19,6 @@
 		<PackageTags>encryption;security;e2ee;double-ratchet;x3dh;messaging</PackageTags>
 		<PackageReadmeFile>README.md</PackageReadmeFile>
 		<PackageLicenseExpression>AGPL-3.0-or-later</PackageLicenseExpression>
-		<PackageLicenseFile>LICENSE</PackageLicenseFile>
 		<PackageProjectUrl>https://github.com/rbenzing/LibEmiddle</PackageProjectUrl>
 		<RepositoryUrl>https://github.com/rbenzing/LibEmiddle</RepositoryUrl>
 		<RepositoryType>git</RepositoryType>