docs: address upstream plan review

[ashfulcra]

Summary

• narrow Wave 1 additive language to acknowledge durable derived state without changing existing upstream file semantics
• reframe Track 2 so Fulcra-owned coord-engine/PyPI is the preferred initial ask and fulcra-api folding is a later convergence target
• add standalone posture, bundled-skill road-not-taken, and DESIGN.md operational-scope requirements

Verification

• git diff --check

Bus task: TASK-20260705-review-verdict-changes-o-0c2a7817

[ashfulcra]

Ported to fulcra-tools (branch pr39-port) with 3-way reconciliation against the post-move 07. Note: the Track-2 reorder is a pitch-strategy change — held for Ash's explicit sign-off there. This repo is retired; future PRs → ashfulcra/fulcra-tools.