feat(docker): add Docker container for the agent (salvage #1841) (#3668)

Adds a complete Docker packaging for Hermes Agent:
- Dockerfile based on debian:13.4 with all deps
- Entrypoint that bootstraps .env, config.yaml, SOUL.md on first run
- CI workflow to build, test, and push to DockerHub
- Documentation for interactive, gateway, and upgrade workflows

Closes #850, #913.

Changes vs original PR:
- Removed pre-created legacy cache/platform dirs from entrypoint
  (image_cache, audio_cache, pairing, whatsapp/session) — these are
  now created on demand by the application using the consolidated
  layout from get_hermes_dir()
- Moved docs from docs/docker.md to website/docs/user-guide/docker.md
  and added to Docusaurus sidebar

Co-authored-by: benbarclay <benbarclay@users.noreply.github.com>

Dockerfile

@@ -0,0 +1,20 @@
+FROM debian:13.4
+
+RUN apt-get update
+RUN apt-get install -y nodejs npm python3 python3-pip ripgrep ffmpeg gcc python3-dev libffi-dev
+
+COPY . /opt/hermes
+WORKDIR /opt/hermes
+
+RUN pip install -e ".[all]" --break-system-packages
+RUN npm install
+RUN npx playwright install --with-deps chromium
+WORKDIR /opt/hermes/scripts/whatsapp-bridge
+RUN npm install
+
+WORKDIR /opt/hermes
+RUN chmod +x /opt/hermes/docker/entrypoint.sh
+
+ENV HERMES_HOME=/opt/data
+VOLUME [ "/opt/data" ]
+ENTRYPOINT [ "/opt/hermes/docker/entrypoint.sh" ]