DR-089 — Under Intent, the plan/decomposition surface is the workspace spec-note; the {N.4} PLAN.md artefact is retired

Under Intent, the plan/decomposition surface is the workspace spec-note; the {N.4} PLAN.md artefact is retired. RESEARCH {N.1} / PRODUCT {N.2} / TECH {N.3} remain docs-site artefacts. Reaffirmed by owner S499 after the S498 audit found spec-skill drift; the contradicting skills (write-tech-spec, write-product-spec, research) were swept S499.