Delete shell scripts and simplify Dockerfile

## Parent PRD

#1660

## What to build

Replace the current Dockerfile (Amazon Linux base with manual Node installation) with a `node:24-alpine` based image. Delete all shell scripts: `process-environment.sh`, `docker-entrypoint.sh`, `setup-ssl.sh`. Remove the `NEPTUNE_NOTEBOOK` build arg and all conditional logic around it.

The entrypoint becomes `node dist/node-server.js`. The server serves the client at `/` (no `/explorer` virtual path). Config is provided via volume mount with `GE_CONFIG` env var.

Update the sample Docker Compose files to use the new configuration approach.

## Acceptance criteria

- [ ] Dockerfile uses `node:24-alpine` base image
- [ ] `process-environment.sh` deleted
- [ ] `docker-entrypoint.sh` deleted
- [ ] `setup-ssl.sh` deleted
- [ ] `NEPTUNE_NOTEBOOK` build arg and all conditional logic removed
- [ ] Entrypoint is `node dist/node-server.js`
- [ ] Client served at `/` instead of `/explorer`
- [ ] Sample Docker Compose files updated with volume-mounted config
- [ ] Docker image builds and starts successfully

## Blocked by

- Blocked by #1662

## User stories addressed

- User story 2
- User story 6

## Related Issues

- Part of #1660

Start with the current Dockerfile and the sample Docker Compose files, then inspect process-environment.sh, docker-entrypoint.sh, and setup-ssl.sh to understand their roles. Apply the listed image, entrypoint, routing, configuration, and cleanup changes, then verify that the Docker image builds and starts successfully and that the Compose examples use volume-mounted configuration.

Written by the indexing model from the issue text.