Add Evan's Devcontainer Features to collection index

[esimkowitz]

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

• Related Issue #
• Closes #

Description

This adds my collection of devcontainer features, including fish bundled with Starship and persistent data, direnv, and ssh signing for git (and soon Claude Code persistence).

Collection checklist

If your PR contributes a new collection, please utilize this 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.