Add release: publish tagged releases on the mirror servers

`release [@name ...] <tag> [notes]` does the whole chain in one step —
create the annotated tag, push it to the internal server, then push it to
each selected mirror and turn it into a release object there. Target
selection reuses pushremote's @name mechanism, so the two behave alike.

Notes are generated when none are given: the tag's own annotation when it
carries more than the default, otherwise the commit subjects since the
previous tag, capped at 50 lines. `tag add v1.0 "why this exists"` now
takes a message, which is what that fallback reads; before, the
annotation was always just the tag name.

Tags ending in -rc/-alpha/-beta/-pre are marked as pre-releases on Gitea
and GitHub. Releasing the same tag twice updates the existing release;
a tag that already points at a different commit stops the command, since
moving a published tag makes one version mean different things per
server. A repository that is not on the mirror yet is reported instead of
being created as a side effect.

Binary assets are deliberately out of scope: Gitea attaches them to the
release, GitHub uses a separate upload host, and GitLab does not host
them at all but wants a link into its package registry.

The providers differ in path shape and field names -- GitLab addresses
projects by URL-encoded path, calls the notes "description" and has no
pre-release flag -- so this comes with a recording httptest stand-in that
asserts the exact requests for all three. That harness also covers
authUser, repoExists and the auth header forms, which had no test at all.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

commands.go

@@ -285,6 +285,9 @@ func runCommandDepth(line string, depth int) bool {
 	case "pushremote": // mirror the repo to a public git server via its API
 		handlePushRemote(strings.Join(fields[1:], " "))
 
+	case "release": // tag a commit and publish it as a release on the mirrors
+		handleRelease(strings.Join(fields[1:], " "))
+
 	case "edit": // interactively edit the last N commits
 		if !requireRepo() {
 			break
@@ -516,7 +519,14 @@ func runCommandDepth(line string, depth int) bool {
 		sub := word(words, 1)
 		switch {
 		case sub == "add" && word(words, 2) != "":
-			if gitOK(DIR, "tag", "-a", words[2], "-m", words[2]) {
+			// `tag add v1.0 why this exists` annotates with that text; without
+			// one the tag name is the message, as before. The annotation is
+			// what `release` falls back to for its notes.
+			msg := words[2]
+			if len(fields) > 3 {
+				msg = strings.Join(fields[3:], " ")
+			}
+			if gitOK(DIR, "tag", "-a", words[2], "-m", msg) {
 				gitOK(DIR, "push", "origin", words[2])
 			}
 		case sub == "checkout" && word(words, 2) != "":
@@ -697,6 +707,7 @@ var helpItems = []struct{ cmd, desc string }{
 	{"init", "make new repository from current directory"},
 	{"push [comment]", "push changes to git server"},
 	{"pushremote [@name] [desc]", "mirror repo to the public server(s) (gitea/github/gitlab)"},
+	{"release <tag> [notes]", "tag and publish a release on the public server(s)"},
 	{"pull", "pull changes from git server"},
 	{"fetch", "fetch changes from git server"},
 	{"status [-a]", "short git status (-a: overview of all projects)"},
@@ -714,7 +725,7 @@ var helpItems = []struct{ cmd, desc string }{
 	{"login", "connect to git server"},
 	{"count", "count lines in project"},
 	{"tag", "show tags"},
-	{"tag add <tag>", "add tag"},
+	{"tag add <tag> [msg]", "add tag (msg becomes the annotation)"},
 	{"tag checkout <tag>", "checkout tag"},
 	{"tag delete <tag>", "delete tag"},
 	{"alias [name [cmd]]", "list, show or define an alias ($1..$N, $* args)"},