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>

.dockerignore

@@ -0,0 +1,13 @@
+# Git
+.git
+.gitignore
+.gitmodules
+
+# Dependencies
+node_modules
+
+# CI/CD
+.github
+
+# Environment files
+.env