Implement XBPS packaging lifecycle for Void Linux (issue #85)

Add native XBPS package support with runit service lifecycle:
- packaging/xbps/install.sh: migration guard, fresh install (dormant),
  upgrade (snapshot, migrate, config preservation)
- packaging/xbps/remove.sh: sanctioned disable, purge (full cleanup)
- Makefile: package-xbps target with dependencies and config files
- tests/test_packaging.py: 5 XBPS-specific tests + updated shared tests

Acceptance criteria addressed:
- Fresh install remains dormant; runit down marker set
- Upgrade snapshots and migrates observation history safely
- Removal performs sanctioned pause and retains history
- Migration guard blocks install over make-install remnants
- Debian/RPM regressions verified via existing shared tests

Co-authored-by: CommandCodeBot <noreply@commandcode.ai>

packaging/xbps/install.sh

@@ -0,0 +1,68 @@
+#!/bin/sh
+# XBPS INSTALL script — post-install and post-upgrade paths.
+#
+# Arguments: $1=ACTION $2=PKGNAME $3=VERSION $4=UPDATE $5=CONF_FILE $6=ARCH
+#
+# Actions: pre (before files extracted), post (after files extracted)
+# UPDATE: "yes" on upgrade, "no" on fresh install
+set -eu
+
+STORE_DIR="/var/lib/fenris"
+STORE_DB="${STORE_DIR}/observations.db"
+STORE_BAK="${STORE_DIR}/observations.db.bak"
+RUNTIME_PYTHON="/usr/bin/python3"
+VENDOR_DIR="/opt/fenris/vendor"
+
+ACTION="$1"
+UPDATE="$4"
+
+case "${ACTION}" in
+    pre)
+        # Migration guard — abort if make-install remnants detected
+        MARKER="/var/lib/fenris/manifest.txt"
+        if [ -f "${MARKER}" ]; then
+            echo >&2
+            echo >&2 "Fenris make-install remnants detected — refusing to install."
+            echo >&2
+            echo >&2 "Migrate to the package with:"
+            echo >&2 "  sudo make uninstall   # removes make-install files, preserves store + config"
+            echo >&2 "  sudo xbps-install fenris"
+            echo >&2
+            echo >&2 "See: https://git.bongbetic.com/xavierk/Fenris/blob/main/docs/spec/release-packaging.md#9-migration-from-make-install-systems"
+            echo >&2
+            exit 1
+        fi
+        ;;
+    post)
+        if [ "${UPDATE}" = "yes" ]; then
+            # Upgrade — snapshot, migration, runit-aware reload
+            if [ -f "${STORE_DB}" ]; then
+                cp "${STORE_DB}" "${STORE_BAK}" 2>/dev/null || true
+            fi
+            if [ -d "${VENDOR_DIR}" ] && [ -f "${STORE_DB}" ]; then
+                PYTHONPATH="${VENDOR_DIR}" "${RUNTIME_PYTHON}" -c "
+from fenris.store import migrate_to_latest
+from pathlib import Path
+n = migrate_to_latest(Path('${STORE_DB}'))
+print(f'Fenris migration: {n} step(s) applied') if n else None
+" 2>&1 || echo "Fenris: migration skipped (store not yet initialized)"
+            fi
+            # Ensure log directory exists on upgrade
+            mkdir -p /var/log/fenris-collect
+            chown fenris:fenris /var/log/fenris-collect 2>/dev/null || true
+        else
+            # Fresh install — runit service setup
+            groupadd -f fenris
+            install -d -o root -g fenris -m 2770 "${STORE_DIR}" 2>/dev/null || true
+            # Mark runit service as dormant (down) for fresh install
+            if [ -d /etc/sv/fenris-collect ] && [ ! -e /var/service/fenris-collect ]; then
+                touch /etc/sv/fenris-collect/down
+            fi
+            # Ensure log directory exists
+            mkdir -p /var/log/fenris-collect
+            chown fenris:fenris /var/log/fenris-collect 2>/dev/null || true
+        fi
+        ;;
+esac
+
+exit 0

packaging/xbps/remove.sh

@@ -0,0 +1,34 @@
+#!/bin/sh
+# XBPS REMOVE script — pre-remove and purge paths.
+#
+# Arguments: $1=ACTION $2=PKGNAME $3=VERSION $4=UPDATE $5=CONF_FILE $6=ARCH
+#
+# Actions: pre (before files removed), post (after files removed),
+#          purge (after metadata removed, for config cleanup)
+set -eu
+
+ACTION="$1"
+
+case "${ACTION}" in
+    pre)
+        # Sanctioned disable — close monitoring period
+        if [ -x /usr/libexec/fenris/fenris-monitor ]; then
+            /usr/libexec/fenris/fenris-monitor disable --now 2>/dev/null || true
+        fi
+        # runit: remove the service symlink and mark dormant
+        rm -f /var/service/fenris-collect
+        touch /etc/sv/fenris-collect/down 2>/dev/null || true
+        ;;
+    purge)
+        # Full cleanup — remove config, store, and runit service directories
+        rm -rf /etc/fenris
+        rm -rf /var/lib/fenris
+        if getent group fenris > /dev/null 2>&1; then
+            groupdel fenris 2>/dev/null || true
+        fi
+        rm -rf /etc/sv/fenris-collect 2>/dev/null || true
+        rm -rf /var/log/fenris-collect 2>/dev/null || true
+        ;;
+esac
+
+exit 0