Relicense under AGPL-3.0-or-later

The same licence as ihasmail, which this tool deploys. The network clause
is the part that matters for a deploy tool: a modified copy offered as a
hosted service that deploys for other people has to make its source
available to them, which GPL would not require. Running the tool for your
own host is unaffected.

v2026.9.13 was released under GPL-3.0-or-later and stays so; this applies
from the next release.

README.md

@@ -1,7 +1,7 @@
 # ihasmail-oneshot
 
 [![Latest release](https://img.shields.io/github/v/release/Coffey-Labs/ihasmail-oneshot?sort=date)](https://github.com/Coffey-Labs/ihasmail-oneshot/releases/latest)
-[![License: GPL-3.0-or-later](https://img.shields.io/badge/license-GPL--3.0--or--later-blue)](LICENSE)
+[![License: AGPL-3.0-or-later](https://img.shields.io/badge/license-AGPL--3.0--or--later-blue)](LICENSE)
 
 **One command that turns a Linux Docker host into a working mail server with
 webmail.** It deploys a fresh [Stalwart](https://stalw.art) mail server and a
@@ -869,4 +869,12 @@ public issue.
 
 ## License
 
-GPL-3.0-or-later. See [LICENSE](LICENSE).
+AGPL-3.0-or-later, the same as ihasmail. See [LICENSE](LICENSE).
+
+Running the tool to deploy your own mail host places no obligations on you. The
+licence matters if you modify the tool and offer it to others, including as a
+hosted service that deploys on their behalf: then your modified source must be
+available to them.
+
+`v2026.9.13`, the first release, was published under GPL-3.0-or-later and
+stays under it for anyone who has it. Every later release is AGPL-3.0-or-later.