feat(git): add --server/--check-existing to mkrep for gitea/gitlab/github

mkrep can now pick a git host from --server, $GIT_SERVER, and
$GITEA_URL/$GITEA_HOST/$GITLAB_URL/$GITLAB_HOST (base URL only -- type
must come from --server/$GIT_SERVER, so setting those URL vars for an
unrelated tool can't silently turn a plain mkrep call into a
remote-creating one). Before creating anything it checks via
gh/glab/tea whether the repo already exists and links instead of
recreating it; --check-existing runs just that check and reports
without touching remotes.

functions/_mkrep_default_remote_cmd.fish

@@ -0,0 +1,32 @@
+# Copyright (C) 2026 Rootiest
+# SPDX-License-Identifier: AGPL-3.0-or-later
+
+# SYNOPSIS
+#   _mkrep_default_remote_cmd <type>
+#
+# DESCRIPTION
+#   Prints the default remote-create command template for <type>, used by
+#   mkrep's --server flow when $MKREP_REMOTE_CMD is unset. Same {name},
+#   {user}, {server} placeholders as --new-remote.
+#
+# ARGUMENTS
+#   type   gitea, gitlab, or github
+#
+# RETURNS
+#   The template string, on stdout
+#
+# EXIT STATUS
+#   0  known type
+#   1  unrecognized type
+function _mkrep_default_remote_cmd --argument-names type
+    switch $type
+        case github
+            echo 'gh repo create {name} --private --source=. --remote=origin --push'
+        case gitlab
+            echo 'glab repo create {name} --private --skipGitInit && git remote add origin {server}/{user}/{name}.git && git push -u origin HEAD'
+        case gitea
+            echo 'tea repos create --name {name} --private && git remote add origin {server}/{user}/{name}.git && git push -u origin HEAD'
+        case '*'
+            return 1
+    end
+end