[Feature] Publish to Flathub

[DancingEmptier667]

Is your feature request related to a problem? Please describe. Flathub is the App Store for Linux. It works on almost all major distributions. .deb packages are only supported on Debian-based distros and AppImages are extremely inconvenient and insecure.

Describe the solution you'd like Publish Linkora to Flathub, so it will be much easier to install on Linux.

Describe alternatives you've considered Make a standalone .flatpak file available in GitHub releases.

Additional context Flathub has detailed documentation on how to build and publish software there: https://docs.flathub.org/docs/category/for-app-authors