jj: top alias for `heads(mine)` to look orphan head commits

modules/dev/vcs/jj.nix

···
           "branchesandheads" = "branches | (heads(trunk()::) & mine())";
           "curbranch" = "latest(branches::@- & branches)";
           "nextbranch" = "roots(@:: & branchesandheads)";
+          "top" = "heads(mine())";
         };
         ui = {
           default-command = [