`CatalogStackBase._validate_catalog_url` (inherited by `IntegrationCatalog`)
and `PresetCatalog._validate_catalog_url` checked `parsed.netloc`, which is
truthy for host-less URLs like `https://:8080` (port only) or `https://user@`
(userinfo only). Such URLs slipped past validation despite the error message
promising "a valid URL with a host", then failed later with a confusing fetch
error.
Switch both validators to `parsed.hostname` (None for those inputs), matching
the workflow, step, and bundler catalog validators that already do this.
Add regression tests covering port-only and userinfo-only URLs for both
validators.
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
cb7c36c95b