Shared provider auth status formatting.
Format an auth manager badge for a provider.
Used by the /auth manager, where each provider renders a bracketed,
styled badge (e.g. [stored], [env set: ANTHROPIC_API_KEY], [missing]).
Format a model selector provider-header indicator.
Used by /model, where the indicator is plain text shown next to the
provider name. Returns an empty string for CONFIGURED providers, which
need no indicator.
