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/rpm/preun.sh

@@ -1,16 +1,13 @@
 #!/bin/sh
 # RPM %preun — pre-uninstall scriptlet (spec §7).
-#
-# On erase ($1 -eq 0):  sanctioned disable — close monitoring period.
-# On upgrade ($1 -ge 1): no-op — never interrupt monitoring.
 set -eu
 
 if [ "$1" -eq 0 ]; then
-    # Package is being erased (fully removed), not just upgraded
+    # Package is being erased — sanctioned disable (spec §7)
     if [ -x /usr/libexec/fenris/fenris-monitor ]; then
         /usr/libexec/fenris/fenris-monitor disable --now 2>/dev/null || true
     fi
     systemctl stop fenris-collect.timer 2>/dev/null || true
     systemctl disable fenris-collect.timer 2>/dev/null || true
 fi
-# On upgrade ($1 -ge 1): do nothing — monitoring continues uninterrupted
+# On upgrade ($1 -ge 1): do nothing