Add publish-mcp.sh so the standalone MCP binary stops going stale

Aspire doesn't run or manage src/Novelly.Mcp — it's a separate stdio
process the MCP client spawns from a published binary that nothing
rebuilds automatically. It had drifted 12 days out of date and was
silently missing the service-API-key auth header, causing confusing
401s. Script wraps the existing dotnet publish command via the shared
ensure_dotnet helper; README points at it instead of the raw command.

Also registers a UserSecretsId on Novelly.Api so Auth:ServiceApiKey
can be set locally without landing in appsettings.

src/Novelly.Api/Novelly.Api.csproj

@@ -1,4 +1,4 @@
-<Project Sdk="Microsoft.NET.Sdk.Web">
+<Project Sdk="Microsoft.NET.Sdk.Web">
 
   <ItemGroup>
     <ProjectReference Include="..\Novelly.ServiceDefaults\Novelly.ServiceDefaults.csproj" />
@@ -24,6 +24,7 @@
     <Nullable>enable</Nullable>
     <LangVersion>latest</LangVersion>
     <ImplicitUsings>enable</ImplicitUsings>
+    <UserSecretsId>fb455630-f631-46bb-9c60-0deaf01c593e</UserSecretsId>
   </PropertyGroup>
 
 </Project>