Fontmatrix

A packaging release. It adds an AppImage, a Flatpak changes for compliance with the Flathub standards, and a fix for icons that could not be seen on dark themes.

## New

* AppImage for Linux. It runs on any distribution with glibc 2.34 or newer. It is built with KDE Craft the same way KDE builds its own AppImages, and every tagged release includes it.
* It uses your system's fontconfig, so a current /etc/fonts no longer causes a warning for every file.
* It does not include the Activate for all users option, because an AppImage cannot install the polkit helper that option needs.

## Flatpak

* No home folder access. Files are opened and saved through the desktop's file chooser. The app can only reach two places on your system: ~/.local/share/fonts, for activating fonts, and ~/.config/fontconfig, for hiding system fonts.
* Runtime updated to KDE 6.11.
* No --own-name permission needed. The single-instance D-Bus service now registers under the application ID, com.github.fontmatrix.Fontmatrix.
* CI now checks the manifest and the built repository with flatpak-builder-lint.

## Fixes

* Icons on dark themes. Outside Plasma (the AppImage, other desktops, Windows, m