Add all files needed to package Yaak as a Flatpak for distribution on
Flathub. Uses the deb-extraction approach recommended by Tauri docs:
the manifest downloads the existing .deb release artifact, extracts it,
and installs the binary/resources into the Flatpak /app prefix.
Includes:
- AppStream metainfo.xml with app metadata and branding
- Flatpak manifest (app.yaak.desktop.yml) for x86_64 and aarch64
- Properly sized icons (128/256/512px) named per Flatpak conventions
- Helper script to update manifest hashes for new releases
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
