Summary

Pin the devcontainer base image to a specific version tag and align the Node.js version with copilot-setup-steps for reproducible builds.

Acceptance Criteria

• Base image changed from mcr.microsoft.com/devcontainers/base:ubuntu to mcr.microsoft.com/devcontainers/base:0-ubuntu-22.04
• Node.js feature version changed from "lts" to "20" to match copilot-setup-steps.yml
• Devcontainer features remain at major version pins (:1) for security update coverage
• Existing codespace builds succeed after changes

Technical Details

The current unpinned base image (base:ubuntu) resolves to the latest Ubuntu LTS at build time, which can change without notice and break tool installations. Pinning to 0-ubuntu-22.04 provides stability while still receiving security patches within the Ubuntu 22.04 lifecycle.

Feature major version pins (:1) are appropriate because they receive minor and patch updates automatically, keeping tools current while maintaining API compatibility.