test(integration): add e2e testing suite and infrastructure

Introduces a comprehensive integration testing setup and local development environment.

Changes include:
- Add `docker-compose.yml` for local stack orchestration.
- Add `docker-compose.integration.yml` for the integration test environment.
- Create `mock-upstream` service to simulate external LLM provider responses.
- Implement Go-based end-to-end tests verifying control plane configuration and data plane routing.
- Add `integration_test.sh` for quick connectivity verification.

docker-compose.yml

@@ -1,12 +1,16 @@
+version: "3.8"
+
 services:
   # 1. PostgreSQL Database
   postgres:
     image: postgres:15-alpine
     container_name: ez-postgres
     environment:
-      POSTGRES_USER: ${POSTGRES_USER}
-      POSTGRES_PASSWORD: ${POSTGRES_PASSWORD}
-      POSTGRES_DB: ${POSTGRES_DB}
+      POSTGRES_USER: ${POSTGRES_USER:-postgres}
+      POSTGRES_PASSWORD: ${POSTGRES_PASSWORD:-postgres}
+      POSTGRES_DB: ${POSTGRES_DB:-ezapi}
+    ports:
+      - "5433:5432"
     volumes:
       - postgres_data:/var/lib/postgresql/data
     healthcheck:
@@ -22,6 +26,8 @@ services:
     image: redis:7-alpine
     container_name: ez-redis
     command: redis-server --appendonly yes
+    ports:
+      - "6379:6379"
     volumes:
       - redis_data:/data
     healthcheck:
@@ -39,13 +45,13 @@ services:
       dockerfile: Dockerfile
     container_name: ez-api
     ports:
-      - "${EZ_API_PORT}:${EZ_API_PORT}"
+      - "${EZ_API_PORT:-8080}:8080"
     environment:
-      EZ_API_PORT: ${EZ_API_PORT}
-      EZ_PG_DSN: ${EZ_PG_DSN}
-      EZ_REDIS_ADDR: ${EZ_REDIS_ADDR}
+      EZ_API_PORT: ${EZ_API_PORT:-8080}
+      EZ_PG_DSN: ${EZ_PG_DSN:-host=postgres user=postgres password=postgres dbname=ezapi port=5432 sslmode=disable}
+      EZ_REDIS_ADDR: ${EZ_REDIS_ADDR:-redis:6379}
       EZ_REDIS_PASSWORD: ${EZ_REDIS_PASSWORD}
-      EZ_REDIS_DB: ${EZ_REDIS_DB}
+      EZ_REDIS_DB: ${EZ_REDIS_DB:-0}
     depends_on:
       postgres:
         condition: service_healthy
@@ -61,12 +67,12 @@ services:
       dockerfile: Dockerfile
     container_name: ez-balancer
     ports:
-      - "${EZ_BALANCER_PORT}:${EZ_BALANCER_PORT}"
+      - "${EZ_BALANCER_PORT:-8081}:8081"
     environment:
-      EZ_BALANCER_PORT: ${EZ_BALANCER_PORT}
-      EZ_REDIS_ADDR: ${EZ_REDIS_ADDR}
+      EZ_BALANCER_PORT: ${EZ_BALANCER_PORT:-8081}
+      EZ_REDIS_ADDR: ${EZ_REDIS_ADDR:-redis:6379}
       EZ_REDIS_PASSWORD: ${EZ_REDIS_PASSWORD}
-      EZ_REDIS_DB: ${EZ_REDIS_DB}
+      EZ_REDIS_DB: ${EZ_REDIS_DB:-0}
     depends_on:
       redis:
         condition: service_healthy
@@ -79,4 +85,4 @@ volumes:
 
 networks:
   ez-network:
-    driver: bridge
+    driver: bridge