Move version display to GET /api/health/version in HealthController

Uses GetApplicationVersion(Assembly.GetExecutingAssembly()) — the same
timestamp-based version already logged at startup and baked into the
assembly via the csproj <Version> property. Removes the minimal-API
/version endpoint from web/Program.cs and reverts the web Dockerfile
APP_VERSION build-arg (no longer needed).

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

web/Dockerfile

@@ -13,8 +13,6 @@ FROM mcr.microsoft.com/dotnet/aspnet:10.0 AS final
 WORKDIR /app
 EXPOSE 8080
 ENV ASPNETCORE_URLS=http://0.0.0.0:8080
-ARG APP_VERSION=1.0.0
-ENV APP_VERSION=${APP_VERSION}
 
 COPY --from=build /app/publish .
 ENTRYPOINT ["dotnet", "web.dll"]