Add a desktop client that knows what is installed locally

A web page cannot see the file system, so it can only guess which version of a
tool sits on a workstation. This client can look: it places the files itself and
records their checksum, so on the next start it compares and reports instead of
estimating — including when someone replaced a file by hand.

Python with pywebview, mirroring the meeting-transkriptor: the same
dh-components frontend, shown in a native window through the WebView2 that
Windows already ships. No second browser engine is bundled; the executable is
14 MB rather than the ~150 MB an Electron build would cost.

The frontend is an npm workspace so it shares bibliothek-types with the server.
software-bibliothek.json builds the client, which lets the library distribute it
the same way it distributes every other internal tool.