feat: add 33 skills from vudovn/antigravity-kit

- Added: api-patterns, app-builder, architecture, bash-linux, behavioral-modes,
  clean-code, code-review-checklist, database-design, deployment-procedures,
  docker-expert, documentation-templates, game-development, geo-fundamentals,
  i18n-localization, lint-and-validate, mobile-design, nestjs-expert,
  nextjs-best-practices, nodejs-best-practices, parallel-agents,
  performance-profiling, plan-writing, powershell-windows, prisma-expert,
  python-patterns, react-patterns, red-team-tactics, seo-fundamentals,
  server-management, tailwind-patterns, tdd-workflow, typescript-expert,
  vulnerability-scanner
- Updated README: skill count 179 → 223
- Added credit for vudovn/antigravity-kit (MIT License)

Source: https://github.com/vudovn/antigravity-kit

skills/api-patterns/auth.md

@@ -0,0 +1,24 @@
+# Authentication Patterns
+
+> Choose auth pattern based on use case.
+
+## Selection Guide
+
+| Pattern | Best For |
+|---------|----------|
+| **JWT** | Stateless, microservices |
+| **Session** | Traditional web, simple |
+| **OAuth 2.0** | Third-party integration |
+| **API Keys** | Server-to-server, public APIs |
+| **Passkey** | Modern passwordless (2025+) |
+
+## JWT Principles
+
+```
+Important:
+├── Always verify signature
+├── Check expiration
+├── Include minimal claims
+├── Use short expiry + refresh tokens
+└── Never store sensitive data in JWT
+```