feat(cli): add apply subcommand

internal/cli/diff.go

@@ -0,0 +1,23 @@
+package cli
+
+import (
+	"github.com/spf13/cobra"
+
+	"github.com/lukaszraczylo/harness-sync/internal/adapter"
+)
+
+// NewDiff returns the `diff` subcommand. It is a shorthand for
+// `apply --dry-run` and shows pending changes without writing.
+func NewDiff(reg *adapter.Registry) *cobra.Command {
+	return &cobra.Command{
+		Use:   "diff [harness...]",
+		Short: "Show pending changes (alias for `apply --dry-run`)",
+		RunE: func(cmd *cobra.Command, args []string) error {
+			apply := NewApply(reg)
+			apply.SetOut(cmd.OutOrStdout())
+			apply.SetErr(cmd.ErrOrStderr())
+			apply.SetArgs(append([]string{"--dry-run"}, args...))
+			return apply.Execute()
+		},
+	}
+}