feat(services): open-core community/professional tier split

Pro-tier honeypots load from an optional decnet/services/pro/ subpackage that
the registry auto-discovers when present; the Community build omits it, so the
directory's absence IS the entitlement gate (no runtime licence check). Recurse
subclasses so a pro service may extend a community one. Exclude pro from the
community wheel and git-ignore the path (it lives in the private
decnet-professional repo).

Add LICENSING.md documenting the dual-license: AGPL-3.0-or-later core plus a
commercial EULA for the Professional tier.

LICENSING.md

@@ -0,0 +1,40 @@
+# Licensing
+
+DECNET is **dual-licensed open core**.
+
+## Community (this repository)
+
+DECNET core — everything in this repository — is licensed under the **GNU Affero
+General Public License v3.0 or later (AGPL-3.0-or-later)**. See [LICENSE](./LICENSE).
+
+AGPL (not GPL) is deliberate: DECNET is a network-deployed honeypot platform, so
+the AGPL §13 network-use clause matters — anyone who offers DECNET to others over
+a network must make their source available. GPLv3 would leave that loophole open.
+
+## Commercial / Professional
+
+Because the DECNET Foundation holds copyright in the core, the core is **also
+available under a commercial license**. A commercial core license is what lets
+the proprietary **DECNET Professional** add-on (advanced honeypots, distributed
+separately) be combined and shipped with the core without triggering the AGPL's
+copyleft obligations.
+
+DECNET Professional itself is closed source, licensed under the
+[DECNET Commercial EULA](https://github.com/DECNET-Foundation/decnet-professional),
+and is **not** part of this repository. The open-core build neither contains nor
+depends on it.
+
+| Tier         | Code                                   | License                    |
+|--------------|----------------------------------------|----------------------------|
+| Community    | this repo                              | AGPL-3.0-or-later          |
+| Professional | `decnet/services/pro/` (private repo)  | DECNET Commercial EULA     |
+
+To use DECNET core under terms other than the AGPL, or to obtain DECNET
+Professional, contact **licensing@decnet.cl**.
+
+## Contributing
+
+Contributions to the core are accepted under the AGPL. Because the project is
+dual-licensed, contributors must agree that their contributions may also be
+distributed under the commercial license (a CLA / DCO sign-off). Relicensing
+requires that the Foundation hold or be granted rights to all contributed code.