graceful shutdown on sigterm and sigint

[mooncitydev]

what this fixes

the sidecar never called \Sidecar.Stop()\ from the main process. \systemctl stop, \docker stop, and other supervisors send SIGTERM; without handling that, the process did not cancel the txpool context, close the IPC connection, or stop the monitoring server in an orderly way.

changes

• cmd/sidecar/main.go: register SIGINT and SIGTERM, call \sidecar.Stop()\ so the existing shutdown path runs (context cancel, IPC close, metrics cleanup, monitoring server stop).
• internal/health/server.go: use \http.Server.Shutdown\ with a 10s timeout instead of \Close()\ so in-flight health/metrics requests can finish.

testing

go is not available in this environment; please run \go test ./...\ locally.

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made by mooncitydev