Add Flatpak packaging for Patchwork 5.4.0

Bundle Poncho Wonky (Patchwork 5.4.0) for x86_64 and aarch64 on the
24.08 freedesktop runtime with the Electron BaseApp. Launcher forces
Wayland when a socket is present so the app starts from terminals
outside the desktop session. Pinned versions and checksums live in
versions.sh and are validated by check-versions.sh.

.gitignore

@@ -0,0 +1,4 @@
+.flatpak-builder/
+build-dir/
+repo/
+*.swp