flake: integrate rescue image building into the "check" target

flake.nix

@@ -395,9 +395,12 @@
               RC0=$?
               nix run '.#check.host-configs'
               RC1=$?
+              nix run '.#check.rescue'
+              RC2=$?
               echo "nur: $RC0"
               echo "host-configs: $RC1"
-              exit $(($RC0 | $RC1))
+              echo "rescue: $RC2"
+              exit $(($RC0 | $RC1 | $RC2))
             '');
           };
 
@@ -442,6 +445,13 @@
               ''
             );
           };
+
+          check.rescue = {
+            type = "app";
+            program = builtins.toString (pkgs.writeShellScript "check-rescue" ''
+              nix build -v '.#imgs.rescue' --out-link ./result-rescue-img -j2
+            '');
+          };
         };
 
       templates = {