build(.devcontainer): add lockfile; use bookworm for base image

[Fdawgs]

• Added devcontainer-lock.json to pin github-cli feature version
• Removed redundant git feature (pre-installed in base image)
• Switched base image from default trixie to bookworm for stability

Checklist

• Run npm test
• Documentation has been updated and adheres to the style described in CONTRIBUTING.md
• Commit message adheres to the Conventional commits style, following the @commitlint/config-conventional config

[Copilot]

Pull request overview

This PR updates the repository’s Dev Container configuration to improve stability and reproducibility by pinning feature versions and standardizing the base image.

Changes:

• Switch Dev Container base image from the default Debian “trixie” variant to 20-bookworm.
• Add .devcontainer/devcontainer-lock.json to pin the github-cli feature digest/version.
• Add a Dependabot config entry for the devcontainers ecosystem and ignore the lockfile for Prettier formatting.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
.prettierignore	Excludes the auto-generated Dev Container lockfile from formatting.
.github/dependabot.yml	Adds monthly Dependabot updates for Dev Container features.
.devcontainer/devcontainer.json	Uses the 20-bookworm image and removes the redundant git feature.
.devcontainer/devcontainer-lock.json	Locks the github-cli feature to a specific version/digest.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.