fix: remove Mediator references from dev-cli

The dev-cli was referencing Mediator packages that were removed from
the central package management. The Nuru Endpoint DSL doesn't require
Mediator - it uses its own source generator.

🤖 Generated with [opencode](https://opencode.ai)

Co-Authored-By: opencode <noreply@opencode.ai>

Author: StevenTCramer

tools/dev-cli/Directory.Build.props

@@ -58,11 +58,6 @@
     <!-- Package references -->
     <PackageReference Include="TimeWarp.Amuru" />
     <PackageReference Include="TimeWarp.Nuru" />
-    <PackageReference Include="Mediator.Abstractions" />
-    <PackageReference Include="Mediator.SourceGenerator">
-      <PrivateAssets>all</PrivateAssets>
-      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
-    </PackageReference>
   </ItemGroup>
 
 </Project>