dotnet pack embeds dev-mode frontend bundles — sm pack must force a production Vite build

[antosubash]

Found during module-packaging Session 1 checkpoint.

Packing SimpleModule.FeatureFlags after a dev workspace build put a ~1.3 MB unminified Manage-*.mjs chunk (plus 2.8 MB source map) into the nupkg's staticwebassets. The JsBuild target reuses whatever the last Vite build produced.

sm pack (Session 2) should force a production build (minified, no source maps — or maps stripped from the package) and fail closed if the bundle does not externalize react / react-dom / @inertiajs/react / SimpleModule.UI.