+ automatically refresh README screenshots

[Hawkynt]

What changed

• added a cheap Generate workflow for every non-main working-branch push
• reuse the existing Avalonia headless screenshot tests instead of introducing another rendering path
• validate both generated PNGs before committing them back to the branch
• commit changed screenshots through Hawkynt/RepositoryTemplate/commit-generated-file@v1, preserving signed-commit branch protection
• explicitly dispatch CI when generation advances a branch that already has an open PR

Design

The screenshot implementation already existed in ReadmeScreenshotTests; the missing piece was automatic pre-PR generation. This mirrors the established MassMediaEdit / RepositoryTemplate generated-file pattern and keeps full PR CI focused on verification rather than producing an uncommitted artifact.

Validation

• Generate workflow run 33474507780: success
• existing screenshot test: success
• PNG signature validation: success
• generated-file commit steps: success
• generated-head CI dispatch logic: success

References

• GitHub Actions event behavior for GITHUB_TOKEN-created commits and explicit workflow_dispatch
• Hawkynt/RepositoryTemplate/commit-generated-file@v1
• Hawkynt/MassMediaEdit/.github/workflows/generate.yml

No new dependencies.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Encode branch names before querying the generated head

On branches containing /—for example, the common feature/screenshots naming pattern—gh api sends this interpolated value as multiple URL path segments, while GitHub's Get a branch endpoint expects the branch name as one encoded path parameter. The lookup therefore returns 404 and the Generate job fails before it can dispatch CI; if screenshots were committed with GITHUB_TOKEN, that generated head receives no automatic CI run. Percent-encode branch before constructing this endpoint or obtain the head SHA without embedding the raw ref in the path; gh api --help likewise describes placeholder substitution, not automatic encoding of manually interpolated endpoint components (CLI manual).

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