feat: integrate official Anthropic and Vercel Labs skills

- Add 8 new skills (62 total, up from 58)
- Official Anthropic skills: docx, pdf, pptx, xlsx, brand-guidelines, internal-comms
- Vercel Labs skills: react-best-practices, web-design-guidelines
- Implement dual-versioning: -official/-anthropic and -community suffixes
- Update README with new skill registry and credits
- Regenerate skills_index.json (62 skills validated)
- Add comprehensive walkthrough.md

BREAKING CHANGE: Document skills (docx/pdf/pptx/xlsx) renamed with version suffixes

skills/react-best-practices/rules/server-cache-react.md

@@ -0,0 +1,26 @@
+---
+title: Per-Request Deduplication with React.cache()
+impact: MEDIUM
+impactDescription: deduplicates within request
+tags: server, cache, react-cache, deduplication
+---
+
+## Per-Request Deduplication with React.cache()
+
+Use `React.cache()` for server-side request deduplication. Authentication and database queries benefit most.
+
+**Usage:**
+
+```typescript
+import { cache } from 'react'
+
+export const getCurrentUser = cache(async () => {
+  const session = await auth()
+  if (!session?.user?.id) return null
+  return await db.user.findUnique({
+    where: { id: session.user.id }
+  })
+})
+```
+
+Within a single request, multiple calls to `getCurrentUser()` execute the query only once.