refactor(plan-eng-review): carve review body into on-demand section

Fourth Phase B carve (v2_PLAN.md:220). Moves the 4-section review (Architecture,
Code Quality, Tests, Performance), outside voice, required outputs, and review
report — everything after Step 0 scope — into sections/review-sections.md behind
a single STOP-Read. Step 0 (scope challenge) and EXIT_PLAN_MODE_GATE stay in the
always-loaded skeleton.

Measured: skeleton 106,984 -> 54,892 B (-48.7%). Union preserved. Atomic with
tests + all-host regen (freshness gate): parity flipped to sectioned
(maxSkeletonBytes 62K), plan-eng-review added to SECTIONS_EXTRACTED, gen-skill-docs
reads the union for relocated review/TEST_COVERAGE/dashboard prose. Layer 0 green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

test/helpers/parity-harness.ts

@@ -245,7 +245,13 @@ export const PARITY_INVARIANTS: ParityInvariant[] = [
     minBytes: 80_000,
   },
   {
+    // Carved (v2 plan T9): skeleton + sections/review-sections.md. The 4-section
+    // review, outside voice, and required outputs moved to the section; content
+    // checks run against the union. Skeleton shrank 106,984 -> 54,892 B (-48.7%);
+    // maxSkeletonBytes 62KB = measured + headroom.
     skill: 'plan-eng-review',
+    sectioned: true,
+    maxSkeletonBytes: 62_000,
     mustContain: [
       'Architecture',
       'Code Quality',