Panel: German/English, redesigned sidebar, in-game admins page, Steam Web API key link, RAR/7z save upload (SharpCompress), responsive cards; upload errors return 400; tests

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

MSCO.Server.csproj

@@ -20,6 +20,7 @@
     <FrameworkReference Include="Microsoft.AspNetCore.App" />
     <EmbeddedResource Include="Panel/index.html" LogicalName="panel.index.html" />
     <EmbeddedResource Include="Panel/app.js" LogicalName="panel.app.js" />
+    <EmbeddedResource Include="Panel/i18n.js" LogicalName="panel.i18n.js" />
     <EmbeddedResource Include="Panel/app.css" LogicalName="panel.app.css" />
     <EmbeddedResource Include="Panel/logo.png" LogicalName="panel.logo.png" />
   </ItemGroup>
@@ -30,4 +31,8 @@
     <None Remove="Tests/**" />
   </ItemGroup>
 
+  <ItemGroup>
+    <PackageReference Include="SharpCompress" Version="0.50.4" />
+  </ItemGroup>
+
 </Project>