Fix proto generation failing when new subdirectories are added

The `mv -f` command cannot merge directories — it fails when the
destination directory already exists. Replace with `cp -rf` so that
new proto subdirectories (e.g. nexusservices) are handled correctly.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: rkannan82

Makefile

@@ -61,7 +61,7 @@ go-grpc: clean .go-helpers-installed $(PROTO_OUT)
 		-p grpc-gateway_out=allow_patch_feature=false,$(PROTO_PATHS) \
 		-p go-helpers_out=$(PROTO_PATHS)
 
-	mv -f $(PROTO_OUT)/temporal/api/* $(PROTO_OUT) && rm -rf $(PROTO_OUT)/temporal
+	cp -rf $(PROTO_OUT)/temporal/api/* $(PROTO_OUT) && rm -rf $(PROTO_OUT)/temporal
 
 http-api-docs: go-grpc
 	go run cmd/encode-openapi-spec/main.go \