chore(phase0): eBay 세트 제거 — 문진·문서 admin/API/lib/CONTENT + cheerio

Delete:
- app/api/questionnaire/ (submit/route.ts)
- app/admin/questionnaire/ (page.tsx)
- app/api/admin/questionnaire/ (route.ts + [id]/route.ts)
- app/admin/documents/ (page.tsx)
- app/api/admin/documents/ ([filename]/route.ts)
- lib/ebay-tools/ (crawler.ts·pricing.ts·ai-analyzer.ts·types.ts)
- CONTENT/ebay-tool-{questionnaire,proposal}.html
- CONTENT/ARCHITECTURE_EBAY_PARTS_TOOL.md

Modify:
- app/admin/components/AdminSidebar.tsx: Remove NAV_ITEMS for /admin/documents & /admin/questionnaire
- package.json: Remove cheerio dependency

Verify: npm test (4 files, 20 tests PASS), npm run build OK

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

app/admin/components/AdminSidebar.tsx

@@ -76,18 +76,6 @@ const NAV_ITEMS = [
       </svg>
     ),
   },
-  {
-    href: '/admin/documents',
-    label: '프로젝트 문서',
-    icon: (
-      <svg className="w-5 h-5" fill="none" stroke="currentColor" viewBox="0 0 24 24">
-        <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2}
-          d="M7 21h10a2 2 0 002-2V9.414a1 1 0 00-.293-.707l-5.414-5.414A1 1 0 0012.586 3H7a2 2 0 00-2 2v14a2 2 0 002 2z" />
-        <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2}
-          d="M13 3v5a2 2 0 002 2h4M9 13h6M9 17h4" />
-      </svg>
-    ),
-  },
   {
     href: '/admin/packs',
     label: '팩 자료',
@@ -98,16 +86,6 @@ const NAV_ITEMS = [
       </svg>
     ),
   },
-  {
-    href: '/admin/questionnaire',
-    label: '질문지 응답',
-    icon: (
-      <svg className="w-5 h-5" fill="none" stroke="currentColor" viewBox="0 0 24 24">
-        <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2}
-          d="M9 5H7a2 2 0 00-2 2v12a2 2 0 002 2h10a2 2 0 002-2V7a2 2 0 00-2-2h-2M9 5a2 2 0 002 2h2a2 2 0 002-2M9 5a2 2 0 012-2h2a2 2 0 012 2m-3 7h3m-3 4h3m-6-4h.01M9 16h.01" />
-      </svg>
-    ),
-  },
   {
     href: '/admin/marketing',
     label: '마케팅 에셋',