Standardize exit codes and behaviors

Adjust exit codes and abort handling across multiple PVE helper scripts to provide clearer outcomes for automation and interactive flows. Changes include:

- container-restore-from-backup.sh, core-restore-from-backup.sh: return 235 when no backups found (was 1).
- fstrim.sh: treat user cancellation of non-ext4 warning as non-error (exit 0 instead of 1).
- kernel-clean.sh: treat no selection or user abort as non-error (exit 0 instead of 1).
- lxc-delete.sh: return 234 when no containers are present; treat no selection as non-error (exit 0).
- nic-offloading-fix.sh: use specific non-zero codes for root check and tool install failures (exit 104, 237) and 236 when no matching interfaces (was 1).
- pbs_microcode.sh, post-pmg-install.sh, post-pbs-install.sh: use distinct exit codes (232 and 105) for detected VM/PVE/unsupported distro conditions instead of generic 1.

These modifications make scripts return distinct codes for different failure modes and ensure user-initiated aborts or benign conditions exit with 0 where appropriate.

tools/pve/kernel-clean.sh

@@ -57,7 +57,7 @@ done
 
 if [ ${#kernels_to_remove[@]} -eq 0 ]; then
   echo -e "${RD}No valid selection made. Exiting.${CL}"
-  exit 1
+  exit 0
 fi
 
 # Confirm removal
@@ -66,7 +66,7 @@ printf "%s\n" "${kernels_to_remove[@]}"
 read -rp "Proceed with removal? (y/n): " confirm
 if [[ "$confirm" != "y" ]]; then
   echo -e "${RD}Aborted.${CL}"
-  exit 1
+  exit 0
 fi
 
 # Remove kernels