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>

apisix/conf/config.yaml

@@ -0,0 +1,15 @@
+# APISIX configuration
+apisix:
+  node_listen: 9080
+  enable_admin: false
+
+deployment:
+  role: data_plane
+  role_data_plane:
+    config_provider: yaml
+
+plugin_attr:
+  prometheus:
+    export_addr:
+      ip: 0.0.0.0
+      port: 9091