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>

website/docs/user-guide/docker.md

@@ -0,0 +1,56 @@
+# Hermes Agent — Docker
+
+Want to run Hermes Agent, but without installing packages on your host? This'll sort you out.
+
+This will let you run the agent in a container, with the most relevant modes outlined below.
+
+The container stores all user data (config, API keys, sessions, skills, memories) in a single directory mounted from the host at `/opt/data`. The image itself is stateless and can be upgraded by pulling a new version without losing any configuration.
+
+## Quick start
+
+If this is your first time running Hermes Agent, create a data directory on the host and start the container interactively to run the setup wizard:
+
+```sh
+mkdir -p ~/.hermes
+docker run -it --rm \
+  -v ~/.hermes:/opt/data \
+  nousresearch/hermes-agent
+```
+
+This drops you into the setup wizard, which will prompt you for your API keys and write them to `~/.hermes/.env`. You only need to do this once. It is highly recommended to set up a chat system for the gateway to work with at this point.
+
+## Running in gateway mode
+
+Once configured, run the container in the background as a persistent gateway (Telegram, Discord, Slack, WhatsApp, etc.):
+
+```sh
+docker run -d \
+  --name hermes \
+  --restart unless-stopped \
+  -v ~/.hermes:/opt/data \
+  nousresearch/hermes-agent gateway run
+```
+
+## Running interactively (CLI chat)
+
+To open an interactive chat session against a running data directory:
+
+```sh
+docker run -it --rm \
+  -v ~/.hermes:/opt/data \
+  nousresearch/hermes-agent
+```
+
+## Upgrading
+
+Pull the latest image and recreate the container. Your data directory is untouched.
+
+```sh
+docker pull nousresearch/hermes-agent:latest
+docker rm -f hermes
+docker run -d \
+  --name hermes \
+  --restart unless-stopped \
+  -v ~/.hermes:/opt/data \
+  nousresearch/hermes-agent
+```