feat(cli): add apply subcommand

internal/cli/root.go

@@ -1,7 +1,13 @@
 // Package cli provides the cobra command tree for harness-sync.
 package cli
 
-import "github.com/spf13/cobra"
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+
+	"github.com/spf13/cobra"
+)
 
 func NewRoot(version string) *cobra.Command {
 	return &cobra.Command{
@@ -11,3 +17,16 @@ func NewRoot(version string) *cobra.Command {
 		SilenceUsage: true,
 	}
 }
+
+// resolveRoot returns the canonical root: the flag value when non-empty,
+// else $HOME/.config/harness-sync.
+func resolveRoot(flag string) (string, error) {
+	if flag != "" {
+		return flag, nil
+	}
+	home, err := os.UserHomeDir()
+	if err != nil {
+		return "", fmt.Errorf("resolve home dir: %w", err)
+	}
+	return filepath.Join(home, ".config", "harness-sync"), nil
+}