Create a new flatpak for the standalone version of cardinal

Either have it be completely separated from this original "plugin" flatpak or if possible make the standalone version the main one. This would make it more discoverable in major linux flatpak app store apps such as bazaar with the plugin variant attached as an add-on. This is similar to how cardinal is already packaged where you have cardinal-standalone and cardinal-data and then if you want a clap you get cardinal-clap-plugin (not exactly how it is but to illustrate the idea).

The issue names no files or tests; start by inspecting the repository's existing Flatpak manifest and how the current plugin package refers to Cardinal. Compare the package layout with cardinal-standalone, cardinal-data, and cardinal-clap-plugin, then verify that the standalone app is discoverable separately while the plugin variant remains an add-on.

Written by the indexing model from the issue text.