FE-864: Plan orchestrator brownfield enhancements

Add the full-cook-orchestrator frontiers to memory/PLAN.md as a planning
baseline. Arc 1 (brunch-detect, harness-dep-install, app-runtime-probe,
integration-oracle, brownfield-promotion, brunch-ship + dogfood-spike) and
Arc 2 (interactive-recovery, intent-conformance-oracle, adaptive-replan),
plus the separate transformation-orchestrator line. Records the cook-time
grounding decision, the greenfield-protecting invariant, the kitchen-brigade
CLI surface, and the unpublished pi-thread coordination note.

Docs-only; downstream feature branches stack on this.

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Co-Authored-By: Claude <noreply@anthropic.com>

Author: kostandinang