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/install

@@ -0,0 +1,17 @@
+# Binary files
+target/release/bootupd usr/libexec/
+
+# Systemd service
+systemd/bootloader-update.service usr/lib/systemd/system/
+
+# Documentation
+README.md usr/share/doc/deb-bootupd/
+deb-bootupd.md usr/share/doc/deb-bootupd/
+VERSION.md usr/share/doc/deb-bootupd/
+
+# Manual pages
+debian/man/bootupctl.1 usr/share/man/man1/
+
+# Man pages (if available)
+# debian/bootupd.1 usr/share/man/man1/
+# debian/bootupctl.1 usr/share/man/man1/