feat: headless-first rewrite with automated release pipeline

[aanas-sayed]

Summary

• Migrate Dockerfile to debian:bookworm-slim + winehq-stable (no-install-recommends)
• Add entrypoint.sh with Wine priming + Xvfb startup for reliable headless operation
• Add ltspice wrapper script (/usr/local/bin/ltspice)
• Add test workflow (test.yml) with simulation validation and artifact upload
• Add release workflow (release.yml) with ETag-based LTspice change detection, YYYY.MM.DD / YYYY.MM.DD-<sha> / latest tagging, and Docker Hub push
• Reduced image content size
• Rewrite README for headless-first usage with X11 forwarding docs for Linux/macOS