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/database-design/migrations.md

@@ -0,0 +1,48 @@
+# Migration Principles
+
+> Safe migration strategy for zero-downtime changes.
+
+## Safe Migration Strategy
+
+```
+For zero-downtime changes:
+│
+├── Adding column
+│   └── Add as nullable → backfill → add NOT NULL
+│
+├── Removing column
+│   └── Stop using → deploy → remove column
+│
+├── Adding index
+│   └── CREATE INDEX CONCURRENTLY (non-blocking)
+│
+└── Renaming column
+    └── Add new → migrate data → deploy → drop old
+```
+
+## Migration Philosophy
+
+- Never make breaking changes in one step
+- Test migrations on data copy first
+- Have rollback plan
+- Run in transaction when possible
+
+## Serverless Databases
+
+### Neon (Serverless PostgreSQL)
+
+| Feature | Benefit |
+|---------|---------|
+| Scale to zero | Cost savings |
+| Instant branching | Dev/preview |
+| Full PostgreSQL | Compatibility |
+| Autoscaling | Traffic handling |
+
+### Turso (Edge SQLite)
+
+| Feature | Benefit |
+|---------|---------|
+| Edge locations | Ultra-low latency |
+| SQLite compatible | Simple |
+| Generous free tier | Cost |
+| Global distribution | Performance |