fix(backup): dereference symlinks using rsync -L flag

Add the -L (--copy-links) flag to rsync calls for systemd units and cron
directories to dereference symlinks into actual target files, resolving
"Operation not permitted" failures on non-POSIX target filesystems.

host_backup.sh

@@ -95,7 +95,7 @@ if [ -f "/etc/crontab" ]; then
 fi
 
 if [ -d "/etc/cron.d" ]; then
-    rsync -a /etc/cron.d "$CURRENT_BACKUP_DIR/cron/"
+    rsync -aL /etc/cron.d "$CURRENT_BACKUP_DIR/cron/"
     echo "Backed up: /etc/cron.d directory"
 fi
 
@@ -103,7 +103,7 @@ fi
 # Task 4: Backup Custom Systemd Units & Services
 # ==============================================================================
 if [ -d "$SYSTEMD_SOURCE" ]; then
-    rsync -a "$SYSTEMD_SOURCE/" "$CURRENT_BACKUP_DIR/systemd/"
+    rsync -aL "$SYSTEMD_SOURCE/" "$CURRENT_BACKUP_DIR/systemd/"
     echo "Backed up: $SYSTEMD_SOURCE"
 else
     echo "Warning: Systemd directory '$SYSTEMD_SOURCE' not found." >&2