Single-runner workflow: test on every push; on v* tags cross-compile tefterd
for all platforms, build the Linux desktop app, and publish a Gitea release
via gitea.com/actions/release-action. Drop the GitHub workflow; document the
runner requirement and manual macOS/Windows desktop builds in the README.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
SVG source in frontend/public/icon.svg, rendered to 192/512/maskable PNGs
and desktop/build/appicon.png; SVG favicon with PNG fallback; icons added
to the service-worker precache.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>