feat: add debian packaging, CI/CD and update script

- Add debian/ packaging for .deb generation
- Add .forgejo/workflows/build.yml for CI/CD (runner label: docker)
- Add scripts/fullupdater and scripts/fullupdater-update
- Remove obsolete install.sh
- Update .gitignore for debian build artifacts

.gitignore

@@ -22,3 +22,17 @@ wheels/
 .venv
 env/
 venv/
+
+# Debian build artifacts
+debian/files
+debian/full-updater/
+debian/*.debhelper
+debian/*.substvars
+debian/changelog.dch
+*.deb
+*.build
+*.buildinfo
+*.changes
+
+# Cache
+/tmp/full-updater-cache/