chore: add repo essentials and GitHub templates

- Add MIT LICENSE file
- Add CONTRIBUTING.md with skill creation guide
- Add AGENTS.md and CLAUDE.md for AI agent guidelines
- Add issue template for skill requests
- Add PR templates for new skills, updates, and docs
- Update README with links to contributing guide and license

.github/PULL_REQUEST_TEMPLATE/documentation.md

@@ -0,0 +1,15 @@
+## Documentation
+
+## Summary
+
+<!-- What documentation changes are you making? -->
+
+## Files changed
+
+<!-- List the files you're updating -->
+
+## Checklist
+
+- [ ] Links are valid
+- [ ] Formatting is consistent with existing docs
+- [ ] No sensitive data or credentials