refactor(office-hours): carve Phase 5+6 into on-demand section

Third Phase B carve (v2_PLAN.md:216, after ship and plan-ceo-review). Moves
Phase 5 (Design Doc templates) + Phase 6 (tiered relationship handoff) — the
session's output + closing tail, only reached after the conversation and
alternatives are done — into sections/design-and-handoff.md, behind a single
STOP-Read after Phase 4.5. The live conversation (Phases 1-4.5) and the
always-run Important Rules stay in the always-loaded skeleton.

Measured: always-loaded skeleton 118,280 -> 88,975 B (-24.8%). Union preserved.
The carved AUQ is identical to pre-carve (matrix: 7/7 format, substance 5),
and Layer 0 confirms the AUQ format spec stays in the skeleton — the AUQ
paranoid suite de-risked this carve end to end.

Atomic with tests + regen (skill-docs.yml gates gen:skill-docs freshness on
every push, so source + regen + tests land together; --host all regenerates
the inlined non-Claude variants):
- sections/manifest.json: passive registry, one entry.
- parity-harness: office-hours flipped to sectioned, maxSkeletonBytes 96_000
  (measured 88,975 + headroom); content/minBytes run against the union.
- skill-size-budget: office-hours added to SECTIONS_EXTRACTED.
- gen-skill-docs + skill-validation: read the skeleton+sections union for
  office-hours so relocated Phase 5/6 prose still counts.

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

test/helpers/parity-harness.ts

@@ -288,7 +288,15 @@ export const PARITY_INVARIANTS: ParityInvariant[] = [
     minBytes: 30_000,
   },
   {
+    // Carved (v2 plan T9): skeleton SKILL.md + sections/design-and-handoff.md.
+    // Phase 5 (design doc) + Phase 6 (handoff) moved into the section, so
+    // 'design doc' / 'problem statement' now live there — content checks run
+    // against the union. maxSkeletonBytes asserts the always-loaded skeleton
+    // shrank from the ~118KB monolith to ~89KB (measured 88,975 B, -24.8%);
+    // headroom to 96KB so a small skeleton edit doesn't trip CI.
     skill: 'office-hours',
+    sectioned: true,
+    maxSkeletonBytes: 96_000,
     mustContain: ['design doc', 'problem statement'],
     mustHaveHeadings: ['## Preamble', '## When to invoke'],
     maxSizeRatio: 1.05,