Relicense under GPL-3.0-or-later

Replace MIT with the full GNU GPLv3 text, update license metadata in
pyproject.toml (+ trove classifiers) and PKGBUILD, and add
SPDX-License-Identifier headers to all Python modules and shell scripts.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

packaging/PKGBUILD

@@ -5,7 +5,7 @@ pkgrel=1
 pkgdesc="Host intrusion-detection daemon — signature-based detection of reverse shells, LD_PRELOAD rootkits, fileless malware, and persistence tampering"
 arch=('any')
 url="https://github.com/Enodia/enodia-sentinel"
-license=('MIT')
+license=('GPL-3.0-or-later')
 depends=('python>=3.11' 'iproute2' 'procps-ng')
 optdepends=('bpftrace: execve tracing of short-lived processes in snapshots'
             'libnotify: desktop notifications on alert')

packaging/build-package.sh

@@ -1,4 +1,5 @@
 #!/bin/bash
+# SPDX-License-Identifier: GPL-3.0-or-later
 # Build the Arch package from the repo root.
 set -e
 cd "$(dirname "$0")"

packaging/enodia-sentinel.wrapper

@@ -1,4 +1,5 @@
 #!/bin/sh
+# SPDX-License-Identifier: GPL-3.0-or-later
 # Launcher for the Enodia Sentinel Python package.
 # Computes the install prefix from its own location so it works whether
 # installed under /usr or /usr/local, with no pip/site-packages involvement.