Changes the default merge strategy from squash to direct by flipping `directMergeCommitStrategy` in the settings schema and types, with the core implementation in `merger-ref-update-advance.ts`. Also aligns a heartbeat executor test assertion with the FN-5060 deduplication shape. Fusion-Task-Id: FN-5255 Co-authored-by: Fusion (runfusion.ai) <noreply@runfusion.ai> Fusion-Task-Id: FN-5255