ci: support historical Dockerfile targets in rebuild workflow

[henrypark133]

Summary

• detect whether the checked-out Dockerfile defines a runtime stage
• use the runtime target when present and fall back to building the final stage when it is not
• include the detected stage mode in the workflow summary

Why

The v0.24.0 release Dockerfile predates the named runtime stage, so the rebuild workflow failed with target stage "runtime" could not be found when rebuilding that release tag.

[gemini-code-assist]

Note

Gemini is unable to generate a review for this pull request due to the file types involved not being currently supported.

[Copilot]

Pull request overview

Updates the release image rebuild GitHub Actions workflow to handle historical tags whose Dockerfile does not define a named runtime stage, preventing failures when rebuilding older releases (e.g., v0.24.0).

Changes:

• Add a “Detect runtime stage” step that checks whether the checked-out Dockerfile defines AS runtime.
• Conditionally build either the runtime target (when present) or the Dockerfile’s final stage (when not).
• Include the detected stage mode in the workflow run summary.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.