Summary

Adds CLI support for the new metadata list endpoints:

--filter accepts the same CEL expressions as gn asset list (bare RHS auto-quoted via the existing normalizeFilter), and --dry-run/-o json|csv|table work as on the other commands.

Implementation notes

• New api.ListNames client method for the shared {"data":[{"name":...}]} shape.
• Shared runNamesListCommand helper drives all four commands.
• CSV/table output now uses a caller-supplied column label via output.Options.Header — tag, category, blockchain — defaulting to the existing metric label, so gn metric list output is unchanged (PrintCSV/PrintTable signatures remain backward compatible).
• Tests use the existing isolated runCLI helper (HOME=t.TempDir(), pinned Go caches) so they never read the developer's ~/.gn or fire OAuth refresh calls. One test file per command file.

Testing

• Dry-run URL assertions, JSON list output, CEL filter pass-through, CSV/table header labels.
• go test ./... green.