chore(docker-compose): enhance environment variable configuration using interpolation

Author: yshngg

docker-compose.yml

@@ -7,10 +7,10 @@ services:
     depends_on:
       - mongodb
     environment:
-      - MCP_REGISTRY_DATABASE_URL=mongodb://mongodb:27017
-      - MCP_REGISTRY_ENVIRONMENT=test
-      - MCP_REGISTRY_GITHUB_CLIENT_ID
-      - MCP_REGISTRY_GITHUB_CLIENT_SECRET
+      - MCP_REGISTRY_DATABASE_URL=${MCP_REGISTRY_DATABASE_URL:-mongodb://mongodb:27017}
+      - MCP_REGISTRY_ENVIRONMENT=${MCP_REGISTRY_ENVIRONMENT:-test}
+      - MCP_REGISTRY_GITHUB_CLIENT_ID=${MCP_REGISTRY_GITHUB_CLIENT_ID}
+      - MCP_REGISTRY_GITHUB_CLIENT_SECRET=${MCP_REGISTRY_GITHUB_CLIENT_SECRET}
     ports:
       - 8080:8080
     restart: "unless-stopped"