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/postun.sh

@@ -1,20 +1,13 @@
 #!/bin/sh
 # RPM %postun — post-uninstall scriptlet (spec §7).
-#
-# On erase ($1 -eq 0): remove config (unmodified removed, modified as .rpmsave),
-#                       store, backups, and group.
-# On upgrade ($1 -ge 1): daemon-reload only.
 set -eu
 
 if [ "$1" -eq 0 ]; then
-    # Package fully erased
+    # Package fully erased — remove config, store, group
     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
 fi
-
-# Always daemon-reload (units may have been removed)
 systemctl daemon-reload 2>/dev/null || true