fix(ci): restore Docker build workflow

[kasuboski]

What

The docker.yml workflow was dropped during the Gleam rewrite (PR #23 replaced the entire Elixir codebase). The Dockerfile survived, but without this workflow no images are built/published to GHCR — and the live deployment on feedreader-2 uses ghcr.io/kasuboski/feedreader:main.

Changes

Restored the Docker build workflow with:

• All actions SHA-pinned with version comments
• persist-credentials: false on checkout
• Concurrency group with cancel-in-progress: true
• Multi-arch build (linux/amd64, linux/arm64) with GHA cache

Verification

• actionlint validates clean
• Docker build passed: run 27955598494 — image pushed to GHCR

Summary by CodeRabbit

• Chores
  • Automated Docker image building and publishing to GHCR with multi-architecture support (amd64/arm64)

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 614c1719-9b07-4731-b886-fde89593b0ca

📥 Commits

Reviewing files that changed from the base of the PR and between 9380a1e and 1ab1870.

📒 Files selected for processing (1)

• .github/workflows/docker.yml

📜 Recent review details

⏰ Context from checks skipped due to timeout. (1)

• GitHub Check: check

🔇 Additional comments (1)

.github/workflows/docker.yml (1)

1-65: LGTM!

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📝 Walkthrough

Walkthrough

A new GitHub Actions workflow file is added that triggers on branch pushes and v*.*.* tags. It builds and pushes a multi-architecture (amd64/arm64) Docker image to GHCR using Buildx, with GitHub Actions cache, SBOM generation, and metadata-based tagging.

Changes

Docker multi-arch build and publish workflow

Layer / File(s)	Summary
Workflow triggers, permissions, and environment .github/workflows/docker.yml	Defines push triggers for all branches and v*.*.* version tags, sets contents: read and packages: write permissions, configures concurrency cancellation, and declares REGISTRY (ghcr.io) and IMAGE_NAME environment variables.
Multi-arch build and GHCR publish job .github/workflows/docker.yml	Implements the build job: checks out the repo, sets up Buildx, computes Docker metadata/tags via docker/metadata-action, authenticates to GHCR with GITHUB_TOKEN, then builds and pushes a linux/amd64,linux/arm64 image with GHA cache (mode=max) and SBOM generation enabled.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~5 minutes

Possibly related PRs

• kasuboski/feedreader#22: Directly modifies the same .github/workflows/docker.yml file to build and push a multi-architecture Docker image to GHCR with Buildx and metadata tags — essentially the same workflow being added or updated here.

Poem

🐇 Hippity-hop, a Dockerfile's born,
Two arches unite — no image is torn!
AMD and ARM, both pushed with a whirl,
GHCR shines like a bright little pearl.
The bunny ships containers with glee,
v*.*.* tags set the releases free! 🐳

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The PR title 'fix(ci): restore Docker build workflow' accurately summarizes the main change—restoring a previously removed GitHub Actions Docker build workflow.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/restore-docker-workflow

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