Add SSH SFTP backend support

internal/adapters/ssh/integration_test.go

@@ -0,0 +1,39 @@
+package ssh
+
+import (
+	"context"
+	"os"
+	"strconv"
+	"testing"
+)
+
+func TestIntegrationSSHBackendStatRoot(t *testing.T) {
+	host := os.Getenv("DISTRIBUTOR_TEST_SSH_HOST")
+	if host == "" {
+		t.Skip("DISTRIBUTOR_TEST_SSH_HOST is not set")
+	}
+	port := 22
+	if raw := os.Getenv("DISTRIBUTOR_TEST_SSH_PORT"); raw != "" {
+		parsed, err := strconv.Atoi(raw)
+		if err != nil {
+			t.Fatalf("parse DISTRIBUTOR_TEST_SSH_PORT: %v", err)
+		}
+		port = parsed
+	}
+	backend, err := New(context.Background(), Options{
+		Host:          host,
+		User:          os.Getenv("DISTRIBUTOR_TEST_SSH_USER"),
+		Port:          port,
+		Root:          os.Getenv("DISTRIBUTOR_TEST_SSH_PATH"),
+		KeyFile:       os.Getenv("DISTRIBUTOR_TEST_SSH_KEY_FILE"),
+		KnownHosts:    os.Getenv("DISTRIBUTOR_TEST_SSH_KNOWN_HOSTS"),
+		HostKeyPolicy: HostKeyPolicyStrict,
+	})
+	if err != nil {
+		t.Fatalf("New() error = %v", err)
+	}
+	defer backend.Close()
+	if _, err := backend.Stat(context.Background(), ""); err != nil {
+		t.Fatalf("Stat(root) error = %v", err)
+	}
+}