Add GitHub Actions workflow for automated Docker builds

[willnewby]

Summary

• Adds GitHub Actions workflow for automated multi-architecture Docker builds
• Workflow validates builds on PRs and publishes to GHCR on merges to main
• Adds net-tools package to Dockerfile for additional networking utilities
• Adds CLAUDE.md project documentation

Changes

GitHub Actions Workflow (.github/workflows/docker-build.yml)

• Builds for linux/amd64, linux/arm/v7, and linux/arm64/v8 platforms
• On pull requests: validates the build without pushing
• On push to main: builds and pushes to ghcr.io/willnewby/kshell
• Tags images with both latest and {DATE}-{GITSHA} format
• Uses GitHub Actions cache for faster subsequent builds
• Authenticates to GHCR using built-in GITHUB_TOKEN (no secrets required)

Dockerfile

• Added net-tools package for additional networking utilities (netstat, ifconfig, etc.)

CLAUDE.md

• Added project documentation to assist Claude Code with context about the repository

Test Plan

• Verify the GitHub Actions workflow triggers on this PR
• Check that the Docker build completes successfully for all platforms
• Confirm the build does not attempt to push (PR behavior)
• After merge, verify images are pushed to ghcr.io with correct tags

🤖 Generated with Claude Code