test(app): add headless ViewModel, CLI and localization tests

ViewModels run on Avalonia.Headless: wizard flows, password and file-lock
handling, seed and private-key reveal gating, contacts, settings, sync and
send against the fake server. The CLI entry point is invoked in-process
end to end. Localization checks cover the 7 languages, placeholders and
keys used in sources. Internal seams (UpdateCheck, ProfileOverride) keep
the tests offline.

src/App/PalladiumWallet.App.csproj

@@ -27,4 +27,8 @@
   <ItemGroup>
     <ProjectReference Include="..\Core\PalladiumWallet.Core.csproj" />
   </ItemGroup>
+
+  <ItemGroup>
+    <InternalsVisibleTo Include="PalladiumWallet.Tests" />
+  </ItemGroup>
 </Project>