License peo4c under GPL-3.0-or-later and ship third-party notices

- Add the GPL-3.0 LICENSE and SPDX headers to peo4c's own files.
- Add THIRD_PARTY_NOTICES.md listing every bundled component, its
  license and where its license text lives in the image, plus a
  trademark disclaimer; reference it from the README.
- Ship neo4j-browser's LICENSE, NOTICE.txt and LICENSES.txt with a
  source archive of the built commit, as the GPL requires.
- Ship Apache AGE's LICENSE and NOTICE, which the base image lacks.
- Collect license texts for Python packages whose wheels omit them,
  from PyPI sdists or vendored copies in docker/licenses/.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

THIRD_PARTY_NOTICES.md

@@ -0,0 +1,50 @@
+# Third-party notices
+
+peo4c's own code (the `bridge/`, `docker/` and `tests/` directories and the
+`Dockerfile`) is licensed under the GNU General Public License v3.0 or later;
+see [LICENSE](LICENSE).
+
+The container image built from this repository also contains the third-party
+software below. None of it is stored in this repository: it is downloaded when
+the image is built. Inside the image, license texts are collected under
+`/usr/share/doc/peo4c/`.
+
+| Component | License | Copyright | License text in the image |
+| --- | --- | --- | --- |
+| [neo4j-browser](https://github.com/neo4j/neo4j-browser), built unmodified from the commit pinned in the `Dockerfile` | GPL-3.0-or-later | Neo4j Sweden AB | `/usr/share/doc/peo4c/neo4j-browser/` (`LICENSE`, `NOTICE.txt`) |
+| JavaScript libraries bundled into neo4j-browser | various (MIT, Apache-2.0, BSD, ...) | their respective authors | `/usr/share/doc/peo4c/neo4j-browser/LICENSES.txt` |
+| [Apache AGE](https://github.com/apache/age), from the `apache/age` base image | Apache-2.0 | The Apache Software Foundation; portions Bitnine Co., Ltd. | `/usr/share/doc/peo4c/apache-age/` (`LICENSE`, `NOTICE`) |
+| [PostgreSQL](https://www.postgresql.org/), from the `apache/age` base image | PostgreSQL License | The PostgreSQL Global Development Group, The Regents of the University of California | `/usr/share/doc/postgresql-18/copyright` |
+| Debian GNU/Linux base system and packages, including Python 3 and `python3-psycopg` (LGPL-3.0) | various | their respective authors | `/usr/share/doc/<package>/copyright` |
+| [pgAdmin 4](https://www.pgadmin.org/), installed from PyPI | PostgreSQL License | The pgAdmin Development Team | `/opt/pgadmin/app/LICENSE` |
+| Python packages pgAdmin depends on, and `gunicorn` (MIT) | various | their respective authors | `*.dist-info/` under `/opt/pgadmin/lib/python3*/site-packages/`, or `/usr/share/doc/peo4c/pgadmin-python-licenses/` for packages whose wheel lacks a license file |
+
+## Source code
+
+- **neo4j-browser** is licensed under the GPL, which requires the complete
+  corresponding source to accompany the built application. The image contains
+  it as `/usr/share/doc/peo4c/neo4j-browser/neo4j-browser-source.tar.gz`, an
+  archive of the exact commit that was built. Its dependencies are pinned by
+  the `yarn.lock` inside that archive, and the build steps are in this
+  repository's `Dockerfile`.
+- **peo4c** itself ships as Python source code in `/opt/peo4c/bridge/`. This
+  repository has the rest.
+- **Debian packages:** source is available from
+  [sources.debian.org](https://sources.debian.org/) and the Debian archive.
+
+## Interoperability
+
+The peo4c bridge implements the Bolt protocol and PackStream format from their
+public specifications so that unmodified Neo4j clients can connect. It contains
+no source code from Neo4j. To work with those clients it reports itself as
+"Neo4j" with a Neo4j version number, and it recognises the exact query strings
+that neo4j-browser sends; `tests/smoke_test.py` repeats some of those query
+strings to check compatibility.
+
+## Trademarks
+
+Neo4j is a trademark of Neo4j, Inc. PostgreSQL is a trademark of the PostgreSQL
+Community Association. Apache, Apache AGE and the Apache feather logo are
+trademarks of The Apache Software Foundation. pgAdmin is a trademark of the
+pgAdmin Development Team. peo4c is not affiliated with or endorsed by any of
+them; the names are used only to identify the software it works with.