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/_template.md

@@ -0,0 +1,28 @@
+---
+title: Rule Title Here
+impact: MEDIUM
+impactDescription: Optional description of impact (e.g., "20-50% improvement")
+tags: tag1, tag2
+---
+
+## Rule Title Here
+
+**Impact: MEDIUM (optional impact description)**
+
+Brief explanation of the rule and why it matters. This should be clear and concise, explaining the performance implications.
+
+**Incorrect (description of what's wrong):**
+
+```typescript
+// Bad code example here
+const bad = example()
+```
+
+**Correct (description of what's right):**
+
+```typescript
+// Good code example here
+const good = example()
+```
+
+Reference: [Link to documentation or resource](https://example.com)