ci: build and verify the Docker image on amd64 and arm64

[mgd43b]

Summary

Adds a Docker workflow that builds the image for linux/amd64 and linux/arm64 and verifies each one actually works, plus docs for building a multi-platform image.

One note on the issue's premise: the Dockerfile is not x86-only today. The case "$node_arch" block added in 6358786 already installs the arm64 Rollup/LanceDB packages, and optionalDependencies already lists @lancedb/lancedb-linux-arm64-gnu. I built and ran the image on an M-series Mac with no changes and it works. So the real gap was that nothing exercised the ARM64 path — it could regress silently — and nothing documented it. This PR closes that gap rather than changing the Dockerfile.

Type of Change

• New feature (CI coverage)
• Documentation update

Related Issue

Closes #4

Why native runners instead of --platform linux/amd64,linux/arm64

The issue suggests a single QEMU build with both platforms. I tried that first and it does not work reliably: esbuild is a Go binary, and Go binaries abort under qemu-user partway through the Vite build.

@opendocuments/web:build: fatal error: lfstack.push
@opendocuments/web:build: [vite:esbuild] The service was stopped

So the workflow builds each platform on a native runner instead — ubuntu-latest for amd64, ubuntu-24.04-arm for arm64 (free for public repos). This is also much faster than emulating the monorepo build. docker buildx build --platform linux/amd64,linux/arm64 is still the right command for a user on their own machine, and it is what the README now documents.

Test Plan

Verified locally on an Apple Silicon Mac (linux/arm64, built natively):

• docker buildx build --platform linux/arm64 — succeeds
• docker image inspect --format '{{.Architecture}}' → arm64
• require('@lancedb/lancedb') and better-sqlite3 load and run a real query inside the container → arch: arm64, sqlite rows: 1
• Container boots and GET /healthz returns {"status":"ok"} with HEALTHCHECK reporting healthy, using no model config (it degrades to stub models and still serves)

These are exactly the three checks the workflow runs, so amd64 gets the same treatment on a native x86 runner. I could not verify the amd64 leg locally for the QEMU reason above — that one runs for the first time on this PR.

.github/workflows/docker.yml passes actionlint.

Notes

• The workflow is build-and-verify only — it does not push anywhere. If you'd like it to publish a multi-arch manifest to GHCR on main/tags, I'm happy to add that; I left it out since it's a packaging decision that's yours to make.
• paths: filters keep it off doc-only PRs.
• No changeset: nothing here affects a published package.

[Copilot]

Pull request overview

Adds CI coverage to ensure the repo’s Docker image is continuously built and smoke-tested on both linux/amd64 and linux/arm64, preventing silent regressions in native-module and runtime startup paths. Also documents how to build/publish multi-arch images for end users (including Apple Silicon).

Changes:

• Introduces a new GitHub Actions workflow to build and verify Docker images on native amd64 + arm64 runners.
• Adds README documentation (EN + KO) about architecture support and multi-platform buildx usage.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
README.md	Documents amd64/arm64 support and multi-platform Docker build guidance.
README.ko.md	Korean translation of the new architecture + buildx documentation.
.github/workflows/docker.yml	New CI workflow to build and verify Docker images on amd64 and arm64 runners.

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