feat: headless-first rewrite with CI/CD pipeline

[aanas-sayed]

Summary

Comprehensive overhaul of docker-ltspice to be headless-first with a full CI/CD release pipeline.

Changes

Dockerfile

• Migrated to debian:bookworm-slim base for a smaller image
• Fixed Wine/Xvfb initialisation sequence that caused hangs
• Switched Wine install to --no-install-recommends (~110MB reduction)
• Build-only tools (wget, p7zip-full, unzip) removed after use

Headless operation

• New entrypoint.sh: primes Wine before starting Xvfb to prevent service hangs
• ltspice wrapper script for clean CLI usage

Testing

• test.sh: full batch simulation + .meas result validation
• .github/workflows/test.yml: CI on every push and PR

Release pipeline

• .github/workflows/release.yml: ETag-based LTspice change detection, builds only when MSI changes (or on push/manual trigger), tags as latest, YYYY.MM.DD, and YYYY.MM.DD-<sha>

README

• Rewritten for headless-first usage
• X11 forwarding documented for Linux and macOS (XQuartz)
• Z: drive path guidance added to troubleshooting