Re-run dry run after zvol creation before live run confirmation

When missing zvols are created, the first dry run shows errors
because the zvols don't exist yet. After creation, run a second
dry run so the user sees a clean result before confirming the
live migration.

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

truenas_migrate/cli.py

@@ -447,6 +447,12 @@ def interactive_mode() -> None:
                 host=host, port=port, api_key=api_key, zvols=zvol_sizes,
             ))
             print()
+            print(f"  Re-running dry run to verify zvol creation …")
+            print()
+            dry_summary = asyncio.run(
+                run(argparse.Namespace(**base_ns, dry_run=True), archive_data)
+            )
+            print(dry_summary.report())
 
     if not _confirm(f"Apply these changes to {host}?"):
         print("Aborted – no changes made.")