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>

docker/licenses/Flask-Principal/LICENSE

@@ -0,0 +1,22 @@
+Copyright (c) 2012 Ali Afshar
+
+Permission is hereby granted, free of charge, to any person
+obtaining a copy of this software and associated documentation
+files (the "Software"), to deal in the Software without
+restriction, including without limitation the rights to use,
+copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the
+Software is furnished to do so, subject to the following
+conditions:
+
+The above copyright notice and this permission notice shall be
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
+OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
+HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+OTHER DEALINGS IN THE SOFTWARE.