…-case

Addresses the review comment on PR LambdaTest#4 about rebasing onto api-skill/
after upstream's api/ -> api-skill/ rename (PR LambdaTest#6).

- Renames all 18 api-skill/ subdirectories from mixed-case with spaces
  to lowercase hyphen-case
- Renames references/ (plural) to reference/ (singular) for the 2 api
  skills that had playbook reference directories, matching repo convention
- Updates api-skill/README.md directory tree to reflect new structure
  and fixes relative links to CONTRIBUTING.md and LICENSE
- Fixes typo 'dcoumentation' -> 'documentation' in postman-to-newman

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

… in index

Rebased onto upstream's api/ -> api-skill/ rename (PR LambdaTest#6), applied on
top of PR LambdaTest#4's subdirectory normalization.

- Add languages, category (api-testing), license (MIT), and metadata
  to all 24 api-skill/ SKILL.md files to match the test-skill frontmatter
  standard already enforced by scripts/validate_skills.py for 46 non-api skills
- Update validate_skills.py to scan api-skill/ (was api/) and add
  api-design to VALID_CATEGORIES
- Add 'api-skill' to SKIP_DIRS so nested skills aren't double-counted
- Register all 24 api-skill entries in skills_index.json with full
  descriptions and trigger keywords
- Sort all 70 skills alphabetically, update total_skills to 70

Validation:
  Skills found: 70
  Errors: 0
  Warnings: 47 (expected — api-skills are single-file, no playbooks)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>