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>

README.md

@@ -111,3 +111,15 @@ Neo4j Python driver against a running instance:
 pip install neo4j
 python tests/smoke_test.py neo4j://localhost:7687 postgres secret
 ```
+
+## License
+
+peo4c is free software, licensed under the GNU General Public License v3.0 or
+later; see [LICENSE](LICENSE). The container image bundles third-party software
+under its own licenses, including neo4j-browser (GPL-3.0), Apache AGE
+(Apache-2.0), PostgreSQL and pgAdmin (PostgreSQL License). See
+[THIRD_PARTY_NOTICES.md](THIRD_PARTY_NOTICES.md) for the full list and where
+each license text and source archive is in the image.
+
+Neo4j is a trademark of Neo4j, Inc.; peo4c is not affiliated with or endorsed
+by Neo4j.