fix(deploy): honor configured Go module proxy

Dockerfile

@@ -2,6 +2,8 @@ FROM golang:1.26.5-bookworm AS build
 
 WORKDIR /src
 COPY go.mod go.sum ./
+ARG GOPROXY=https://proxy.golang.org,direct
+ENV GOPROXY=${GOPROXY}
 RUN go mod download
 COPY . ./
 

scripts/containerized_deployment_test.go

@@ -40,6 +40,22 @@ func TestRootInstallerBuildsImageWithoutOperatorImageArgument(t *testing.T) {
 	}
 }
 
+func TestDockerfilePropagatesConfiguredGoProxyToModuleDownload(t *testing.T) {
+	data, err := os.ReadFile("../Dockerfile")
+	if err != nil {
+		t.Fatal(err)
+	}
+	source := string(data)
+	for _, required := range []string{"ARG GOPROXY=", "ENV GOPROXY=${GOPROXY}", "RUN go mod download"} {
+		if !strings.Contains(source, required) {
+			t.Errorf("Dockerfile missing %q", required)
+		}
+	}
+	if !(strings.Index(source, "ENV GOPROXY=${GOPROXY}") < strings.Index(source, "RUN go mod download")) {
+		t.Fatal("Dockerfile must set GOPROXY before downloading modules")
+	}
+}
+
 func TestRDSInitializerOnlyInitializesEmptySchemaAndRejectsInconsistentSchema(t *testing.T) {
 	data, err := os.ReadFile("../deploy/dobotai-dingtalk/rds-schema-init.sh")
 	if err != nil {