fix(packaging): address code review findings

- Upgrade path restarts only fenris-collect.timer, not fenris-collect.service
  (spec §7: "a running oneshot finishes on its old interpreter")
- Remove redundant deb depends override in nfpm.yaml (top-level is sufficient)
- Remove common.sh sourcing — scripts are self-contained to avoid path
  dependency when dpkg/rpm run them from /var/lib/dpkg/info/

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

packaging/postrm.sh

@@ -3,14 +3,12 @@
 #
 # dpkg calls: postrm remove    (after package files removed)
 #             postrm purge     (after conffiles and config removed)
-#             postrm upgrade   (after new version installed)
 set -eu
 
 case "${1:-}" in
     purge)
         rm -rf /etc/fenris
         rm -rf /var/lib/fenris
-        # Remove the fenris group if it exists
         if getent group fenris > /dev/null 2>&1; then
             groupdel fenris 2>/dev/null || true
         fi
@@ -18,6 +16,4 @@ case "${1:-}" in
     remove|upgrade|failed-upgrade|abort-install|abort-upgrade|disappear)
         ;;
 esac
-
-# Always daemon-reload after removal (units may be gone)
 systemctl daemon-reload 2>/dev/null || true