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/app-builder/feature-building.md

@@ -0,0 +1,53 @@
+# Feature Building
+
+> How to analyze and implement new features.
+
+## Feature Analysis
+
+```
+Request: "add payment system"
+
+Analysis:
+├── Required Changes:
+│   ├── Database: orders, payments tables
+│   ├── Backend: /api/checkout, /api/webhooks/stripe
+│   ├── Frontend: CheckoutForm, PaymentSuccess
+│   └── Config: Stripe API keys
+│
+├── Dependencies:
+│   ├── stripe package
+│   └── Existing user authentication
+│
+└── Estimated Time: 15-20 minutes
+```
+
+## Iterative Enhancement Process
+
+```
+1. Analyze existing project
+2. Create change plan
+3. Present plan to user
+4. Get approval
+5. Apply changes
+6. Test
+7. Show preview
+```
+
+## Error Handling
+
+| Error Type | Solution Strategy |
+|------------|-------------------|
+| TypeScript Error | Fix type, add missing import |
+| Missing Dependency | Run npm install |
+| Port Conflict | Suggest alternative port |
+| Database Error | Check migration, validate connection |
+
+## Recovery Strategy
+
+```
+1. Detect error
+2. Try automatic fix
+3. If failed, report to user
+4. Suggest alternative
+5. Rollback if necessary
+```