Add EmperorRAG dev container features (OpenBao)

[EmperorRAG]

What type of PR is this?

• Add a new dev container collection
• Update to an existing dev container collection
• Documentation/spec update
• Other containers.dev site update (UX, layout, etc)

Related Issues

None.

Description

This adds the EmperorRAG dev container collection to the collection index. The collection ghcr.io/emperorrag/devcontainer-features publishes the OpenBao dev container feature (ghcr.io/emperorrag/devcontainer-features/openbao), which runs a local OpenBao vault beside a dev container, writes short-lived tokens for it and can seed it from a sops-encrypted secrets file before any lifecycle hook runs, together with its helper image and the matching template (ghcr.io/emperorrag/devcontainer-templates/openbao). All packages are public on GHCR, published from the repository https://github.com/EmperorRAG/my-private-projects-monorepo, where the feature's documentation and proof records live.

Collection checklist

• Collection name
• Maintainer name
• Maintainer contact link (i.e. link to a GitHub repo, email)
• Repository URL
• OCI Reference (must be the collection root, e.g. ghcr.io/<owner>/<repo> — one entry per repository, not one per Feature; do not include http:// or https://)
• I acknowledge that this collection provides new functionality, distinct from the existing collections part of this index.