Add ce-commit-push-pr and ce-resolve-pr-feedback as coding-mode skill
steps before the merge seam. Per KTD-6 the CE steps own commit/push/PR
creation and feedback resolution; Fusion's merge seam still owns the
board-state merge transition, so the two never race the same branch.
Tests assert the new steps, coding mode, preserved merge seam, and
ordering.
NOTE: the precise handoff between ce-commit-push-pr's PR and Fusion's
workflow-owned board merge (Risk-3) needs verification on a running board.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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