Implements workflow step test mode (FN-5205) by wiring mock dispatch, context forwarding, and routing through executor, merger, and mock provider, plus adding corresponding tests and docs. Also adds broad-scope triage heuristics to improve task-scope detection, touching triage.ts, triage-broad-scope Fusion-Task-Id: FN-5205 Co-authored-by: Fusion (runfusion.ai) <noreply@runfusion.ai> Fusion-Task-Id: FN-5205