fix(fxconfig): defer CloseSend on broadcast stream to prevent connection leak (#209)

[SAY-5]

Fixes #209. OrdererClient.send() opens a gRPC broadcast stream via oc.client.Broadcast(ctx) but never calls CloseSend(). On every error path (Send failure, Recv failure, non-SUCCESS status) and even on the success path, the stream is abandoned. The underlying gRPC connection is held until ctx cancellation rather than released immediately, leaking one stream per call.

Change

tools/fxconfig/internal/client/orderer.go:82, add defer abc.CloseSend() immediately after the stream is successfully opened. CloseSend only signals end-of-send to the server; it doesn't tear down the connection or affect the in-flight Recv, so all four exit paths now release the stream cleanly.

Test plan

• go build ./tools/fxconfig/..., clean
• go vet ./tools/fxconfig/..., clean
• No behaviour change beyond the cleanup; Recv still runs after Send and returns the same status before defer fires