Build & publish the simulator image via GitHub Actions

[YWHyuk]

Summary

Adds a GitHub Actions workflow that builds an Ubuntu-based image with the simulator side fully installed (ASTRA-Sim analytical backend, chakra, python deps — exactly what scripts/install-sim.sh produces on a bare host) and publishes it to GitHub Container Registry.

Files

• scripts/sim.Dockerfile — Ubuntu 24.04 base + scripts/install-sim.sh. apt deps are pre-installed in a dedicated layer so they cache independently of the source-change rebuilds further down.
• .github/workflows/build-sim-image.yml — Builds on every push to main (and PRs / manual dispatch) touching the install paths. Publishes to ghcr.io/<owner>/<repo>/sim with tags latest (main only), sha-<short> (every build), and the branch name for non-main branches. PRs run the build to validate the install path but do not push.
• scripts/README.md — One row added for sim.Dockerfile.

Why

The simulator side has a non-trivial build (~5-10 min for ASTRA-Sim's analytical backend, plus pip / submodule init). A published image lets contributors and CI runs skip that bootstrap and start from a ready-to-use container.

Usage after merge

docker pull ghcr.io/psal-postech/llmservingsimspec/sim:latest
docker run -it --rm -v "$(pwd)":/workspace \
  ghcr.io/psal-postech/llmservingsimspec/sim:latest bash

Test plan

• PR build kicks in (workflow file path is in the trigger filter, so this PR itself triggers it).
• The build completes successfully on ubuntu-latest GHA runner.
• After merge to main, the workflow publishes ghcr.io/psal-postech/llmservingsimspec/sim:latest and a sha- tag. Org / package visibility may need a one-time flip to public on the GHCR package page.
• docker run against the pulled image lands in /workspace with the simulator deps in place; python -m serving --help works without further install.

Notes

• Image size will be ~3-5 GB (ubuntu + apt + python deps + ASTRA-Sim build artifacts). Public GHCR storage is unlimited; private orgs hit a quota.
• Initial build is ~10-15 min on ubuntu-latest; subsequent cached rebuilds ~2-3 min via cache-from: type=gha.
• Independent of Add CPU profiling support to profiler and vLLM CPU install script #27 (CPU profiler). This PR is purely the CI / image artifact.

---

Generated by Claude Code