Add docker-compose support with environment variable configuration

- Create docker-compose.yml with server and agent services
- Add environment variable support to Dockerfiles via entrypoint scripts
- Configure server with ADDR, PORT, USERNAME, PASSWORD vars
- Configure agent with SERVER, INTERVAL, AGENT_ID vars
- Add health check to server service for container orchestration
- Add service dependencies to ensure server starts before agent
- Create .dockerignore to optimize Docker builds
- Update QUICKSTART.md with Docker Compose instructions
- Support running server only, agent only, or full stack
- Support multiple agents with custom identifiers

Dockerfile.agent

@@ -29,6 +29,17 @@ COPY --from=builder /app/nerd-monitor-agent .
 RUN addgroup -D appgroup && adduser -D appuser -G appgroup
 USER appuser
 
+# Create entrypoint script to handle environment variables
+RUN echo '#!/bin/sh\n\
+SERVER=${SERVER:-localhost:8080}\n\
+INTERVAL=${INTERVAL:-15s}\n\
+AGENT_ID=${AGENT_ID:-}\n\
+if [ -z "$AGENT_ID" ]; then\n\
+  exec ./nerd-monitor-agent --server "$SERVER" --interval "$INTERVAL"\n\
+else\n\
+  exec ./nerd-monitor-agent --server "$SERVER" --interval "$INTERVAL" --id "$AGENT_ID"\n\
+fi\n\
+' > /app/entrypoint.sh && chmod +x /app/entrypoint.sh
+
 # Run the agent
-ENTRYPOINT ["./nerd-monitor-agent"]
-CMD ["--server", "localhost:8080"]
+ENTRYPOINT ["/app/entrypoint.sh"]