feat: APISIX gateway with Docker Compose orchestration for stock microservices

- APISIX declarative config with versioned API routes (/api/v1/{service}/...)
- proxy-rewrite for path transformation, CORS global rule, rate limiting (100 req/s)
- Active health checks on all 6 upstream services
- Docker Compose with 11 containers: Redis, PostgreSQL, MongoDB, 6 Python services, APISIX, Next.js frontend
- Environment config via .env.example

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.env.example

@@ -0,0 +1,14 @@
+# === API Keys (from stock-analysis reference project) ===
+DART_API_KEY=your_dart_api_key_here
+KIS_APP_KEY=your_kis_app_key_here
+KIS_APP_SECRET=your_kis_app_secret_here
+KIS_BASE_URL=https://openapivts.koreainvestment.com:9443
+ANTHROPIC_API_KEY=your_anthropic_api_key_here
+
+# === Infrastructure (defaults work with docker-compose) ===
+REDIS_URL=redis://redis:6379/0
+POSTGRES_DSN=postgresql://stock:stock@postgres:5432/stockdb
+MONGODB_URL=mongodb://mongo:27017
+MONGODB_DB=stock_analysis
+LOG_LEVEL=INFO
+LOG_FORMAT=json