DeepDrftShared.Client's wwwroot/js/ was gitignored, so the TS-compiled
parallax.js was absent at build-time manifest generation. MapStaticAssets
serves _content/ exclusively from the build manifest, so the file was
missing from the publish output — requests fell through to the Blazor
HTML handler, producing a text/html MIME-type error in the browser.
DeepDrftPublic audio JS is unaffected because UseStaticFiles() serves
that startup project's physical wwwroot/ directly, bypassing the manifest.
The RCL has no such bypass, so its compiled JS must be present at
manifest-generation time, which requires tracking it in git.
daniel-c-harvey