Use Starlette, uvicorn and websockets; rename Docker files to container ones

Serve neo4j-browser with Starlette and uvicorn (the optional browser extra)
instead of a hand-written HTTP server, and handle Bolt over WebSocket with the
websockets library's Sans-I/O protocol. Rename Dockerfile, .dockerignore and
docker/ to Containerfile, .containerignore and container/.

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

container/licenses/README.md

@@ -0,0 +1,11 @@
+# Vendored license texts
+
+License files for Python packages that pgAdmin depends on whose PyPI releases do
+not include one. `container/collect-python-licenses.py` copies them into the image.
+Directory names are the PyPI project names.
+
+| Package | License | Source of the text |
+| --- | --- | --- |
+| dnspython | ISC | https://github.com/rthalley/dnspython/blob/v2.9.0/LICENSE |
+| Flask-Principal | MIT | https://github.com/mattupstate/flask-principal/blob/0.4.0/LICENSE |
+| ua-parser-builtins | Apache-2.0 | https://github.com/ua-parser/uap-python/blob/master/LICENSE; it bundles data from uap-core: https://github.com/ua-parser/uap-core/blob/master/LICENSE |