Explicitly write a form definition or final submission batch to GitHub through the optional writeback app.

Requires commentary.forms.writeback, the forms.github_writeback license feature, a configured optional GitHub writeback app, an installed repository target, and a valid branch/path target. Submission writeback accepts submissionId or submissionIds, writes one canonical JSON result file per submission in one commit, overwrites existing result paths, can explicitly create target branches with target.createBranch and target.baseBranch, and can optionally open a pull request. Commentary storage remains available when writeback is unavailable.