The releases block carried upstream's 1.0.x history, so a software centre
read the app as newer than every Nightcap tag and would never offer 0.3.x as
an update. Describe the 0.x line instead, and name Nightcap in the project
description.
Rename the desktop entry, metainfo, icons, Flatpak manifest, and SDL app
identity so Nightcap installs side by side with upstream. Build a signed
Flatpak on v* tags, publish the OSTree repo and landing page to GitHub
Pages, and attach the bundle to the release. Release creation tolerates
the AppImage and Flatpak workflows racing on the same tag.