feat(ci): keep only latest PR preview image to reduce storage

[ArtieReus]

Summary

Optimizes GHCR storage usage by automatically deleting old PR preview Docker images after each new build. Only the most recent image per PR is retained during the PR lifecycle, significantly reducing storage costs while maintaining full preview functionality.

Also removes unused AppContent.tsx file from the assets/pr-preview directory.

Changes Made

• Added cleanup-old-images job that runs after successful image builds
• Added image-built and pr-version outputs to build-and-push job for cleanup coordination
• Configured cleanup to use shared GHCR cleanup workflow with exclude-tags to preserve the newly built image
• Updated workflow header comments to reflect new cleanup step
• Updated docs/greenhouse-pr-preview-workflow.md with new job documentation and flow diagram
• Added retention policy documentation for Docker images
• Removed unused assets/pr-preview/AppContent.tsx file

Related Issues

Screenshots (if applicable)

Testing Instructions

1. Create a test PR and add the greenhouse-pr-build label
2. Wait for the initial image to build successfully
3. Push a new commit to the PR
4. Verify that:
   • A new image with the new commit SHA is built and pushed
   • The cleanup-old-images job runs after the build
   • Only the latest image tag exists in GHCR (old image is deleted)
   • The preview deployment works as expected
5. Close the PR and verify all remaining images are cleaned up

Alternative: Review the workflow logic and job conditions in the changed YAML file.

Checklist

• I have performed a self-review of my code.
• I have commented my code, particularly in hard-to-understand areas.
• I have added tests that prove my fix is effective or that my feature works. (N/A - workflow change, tested via actual PR workflow runs)
• New and existing unit tests pass locally with my changes. (N/A - no code changes)
• I have made corresponding changes to the documentation (if applicable).
• My changes generate no new warnings or errors.
• I have created a changeset for my changes. (N/A - workflow file, not a package change)

PR Manifesto

Review the PR Manifesto for best practises.

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Latest commit: 7a78e1e

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[Copilot]

Pull request overview

This PR updates the Greenhouse PR preview workflow to reduce GHCR storage by keeping only the latest preview image per PR, and documents the intended cleanup behavior.

Changes:

• Adds a cleanup-old-images reusable workflow job after PR preview image builds.
• Exposes build outputs used to preserve the newly built image during cleanup.
• Updates Greenhouse PR preview documentation and removes the unused assets/pr-preview/AppContent.tsx.

Reviewed changes

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

File	Description
.github/workflows/build-push-greenhouse-pr-preview.yaml	Adds build outputs and a cleanup job for old PR preview images.
docs/greenhouse-pr-preview-workflow.md	Documents the new image-retention behavior and cleanup job.
assets/pr-preview/AppContent.tsx	Removes an unused PR preview component file.

Comments suppressed due to low confidence (1)

.github/workflows/build-push-greenhouse-pr-preview.yaml:179

• This cleanup job is likely to be cancelled before it can delete anything. The build-and-push job adds the greenhouse-pr-preview label before this dependent job runs, and that label change triggers a new workflow run in the same concurrency group with cancel-in-progress: true, which cancels the still-running/pending cleanup job. Move the cleanup before the label-add step or otherwise prevent the self-trigger from cancelling the cleanup run.

  cleanup-old-images:
    name: Cleanup Old PR Images
    needs: build-and-push
    if: needs.build-and-push.outputs.image-built == 'true'