fix impermanence rollback and add persistent paths

modules/system/impermanence.nix

@@ -19,6 +19,21 @@
       fi
 
       if [ -d /mnt/root ]; then
+        if [ -d /mnt/root-previous ]; then
+          btrfs subvolume delete /mnt/root-previous
+        fi
+        btrfs subvolume snapshot /mnt/root /mnt/root-previous
+
+        while true; do
+          subvols="$(btrfs subvolume list -o /mnt/root | awk '{print $9}')"
+          if [ -z "$subvols" ]; then
+            break
+          fi
+          for subvol in $subvols; do
+            btrfs subvolume delete "/mnt/$subvol"
+          done
+        done
+
         btrfs subvolume delete /mnt/root
       fi
 
@@ -34,8 +49,11 @@
         "/etc/nixos"
         "/etc/ssh"
         "/etc/cups"
+        "/var/lib/bluetooth"
         "/var/lib/cups"
+        "/var/lib/fprint"
         "/var/lib/libvirt"
+        "/var/lib/NetworkManager"
         "/var/lib/secureboot"
         "/var/lib/tailscale"
         "/var/lib/systemd"