Add Debian packaging and update Forgejo workflow

- Add complete Debian packaging configuration (debian/ directory)
- Create build-deb.sh script for building packages
- Update Forgejo workflow to build and upload .deb artifacts
- Add comprehensive version naming for both binary and Debian artifacts
- Update .gitignore to exclude build artifacts and packaging files
- Add PACKAGING.md documentation
- Add test-deb.sh for testing package installation

debian/postrm

@@ -0,0 +1,19 @@
+#!/bin/sh
+set -e
+
+# Post-removal script for deb-bootupd
+# This script runs after the package is removed
+
+# Reload systemd to clean up service references
+if command -v systemctl >/dev/null 2>&1; then
+    deb-systemd-invoke daemon-reload >/dev/null 2>&1 || true
+fi
+
+# Remove the symlink if it still exists
+if [ -L /usr/bin/bootupctl ]; then
+    rm -f /usr/bin/bootupctl
+fi
+
+# Note: We don't remove /boot/bootupd-state.json as it contains
+# important bootloader state that should persist across package removals
+# Users can manually remove it if they want to reset everything