Aligns IMPLEMENTATION_PLAN.md with the cluster-split decision landed in platform/orca-platform PR #6 (6be727d4). 3 cluster repos in §1.1, plane-based env model in §1.8, M1.2 rewritten as VM + repo split gated on legal entity, vm-identity/vm-secrets typos fixed to vm-edge, ERPNext/Frappe HD/M3.2 re-pointed to breakpilot-control, KC repurpose from CERTifAI made explicit. No milestone IDs change; M1.2 sized up M→L.