Fix CI: remove CGO panel builds, match working pipeline pattern

The act runner doesn't have CGO/MinGW available by default. Ship tray +
setup binaries only (panel requires CGO cross-compile, deferred to later).
Also move apt-get install to the step that needs it (zip).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packaging/nfpm.yaml

@@ -11,8 +11,6 @@ license: MIT
 contents:
   - src: ./syncwarden
     dst: /usr/bin/syncwarden
-  - src: ./syncwarden-panel
-    dst: /usr/bin/syncwarden-panel
   - src: ./packaging/linux/syncwarden.desktop
     dst: /etc/xdg/autostart/syncwarden.desktop
     type: config