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/gen-skill-docs.test.ts

@@ -1144,7 +1144,7 @@ describe('Retro plan completion section', () => {
 describe('Plan status footer in preamble', () => {
   test('preamble contains plan status footer as neutral forward reference to EXIT PLAN MODE GATE', () => {
     // Read any skill that uses PREAMBLE
-    const content = fs.readFileSync(path.join(ROOT, 'office-hours', 'SKILL.md'), 'utf-8');
+    const content = readSkillUnion('office-hours'); // carved: Phase 5/6 prose moved to section
     expect(content).toContain('Plan Status Footer');
     expect(content).toContain('GSTACK REVIEW REPORT');
     expect(content).toContain('ExitPlanMode');
@@ -1179,7 +1179,7 @@ describe('make-pdf setup ordering', () => {
 
 describe('Skill invocation during plan mode in preamble', () => {
   test('preamble contains skill invocation plan mode section', () => {
-    const content = fs.readFileSync(path.join(ROOT, 'office-hours', 'SKILL.md'), 'utf-8');
+    const content = readSkillUnion('office-hours'); // carved: Phase 5/6 prose moved to section
     expect(content).toContain('Skill Invocation During Plan Mode');
     expect(content).toContain('precedence over generic plan mode behavior');
     expect(content).toContain('Do not continue the workflow');
@@ -1190,7 +1190,7 @@ describe('Skill invocation during plan mode in preamble', () => {
 // --- {{SPEC_REVIEW_LOOP}} resolver tests ---
 
 describe('SPEC_REVIEW_LOOP resolver', () => {
-  const content = fs.readFileSync(path.join(ROOT, 'office-hours', 'SKILL.md'), 'utf-8');
+  const content = readSkillUnion('office-hours'); // carved: Phase 5/6 prose moved to section
 
   test('contains all 5 review dimensions', () => {
     for (const dim of ['Completeness', 'Consistency', 'Clarity', 'Scope', 'Feasibility']) {
@@ -1226,7 +1226,7 @@ describe('SPEC_REVIEW_LOOP resolver', () => {
 // --- {{DESIGN_SKETCH}} resolver tests ---
 
 describe('DESIGN_SKETCH resolver', () => {
-  const content = fs.readFileSync(path.join(ROOT, 'office-hours', 'SKILL.md'), 'utf-8');
+  const content = readSkillUnion('office-hours'); // carved: Phase 5/6 prose moved to section
 
   test('references DESIGN.md for design system constraints', () => {
     expect(content).toContain('DESIGN.md');
@@ -1256,7 +1256,7 @@ describe('DESIGN_SKETCH resolver', () => {
 // --- {{CODEX_SECOND_OPINION}} resolver tests ---
 
 describe('CODEX_SECOND_OPINION resolver', () => {
-  const content = fs.readFileSync(path.join(ROOT, 'office-hours', 'SKILL.md'), 'utf-8');
+  const content = readSkillUnion('office-hours'); // carved: Phase 5/6 prose moved to section
   const codexContent = fs.readFileSync(path.join(ROOT, '.agents', 'skills', 'gstack-office-hours', 'SKILL.md'), 'utf-8');
 
   test('Phase 3.5 section appears in office-hours SKILL.md', () => {
@@ -1624,7 +1624,7 @@ describe('DESIGN_HARD_RULES resolver', () => {
 // --- Extended DESIGN_SKETCH resolver tests ---
 
 describe('DESIGN_SKETCH extended with outside voices', () => {
-  const content = fs.readFileSync(path.join(ROOT, 'office-hours', 'SKILL.md'), 'utf-8');
+  const content = readSkillUnion('office-hours'); // carved: Phase 5/6 prose moved to section
 
   test('contains outside design voices step', () => {
     expect(content).toContain('Outside design voices');