Respect TLS configuration in registry browser login

[mfridman]

This PR updates doBrowserLogin to use http:// when TLS is disabled instead of always defaulting to https://.

This ensures browser login works correctly in environments where TLS is not configured.

The intention is to match how we initialize clients elsewhere, e.g.,

buf/private/buf/bufcli/connectclient_config.go

Lines 74 to 77 in e6b77ae

	if config.TLS == nil {
	return buftransport.PrependHTTP(address)
	}
	return buftransport.PrependHTTPS(address)

[github-actions]

The latest Buf updates on your PR. Results from workflow Buf CI / buf (pull_request).

Build	Format	Lint	Breaking	Updated (UTC)
✅ passed	✅ passed	✅ passed	✅ passed	Dec 31, 2025, 2:23 PM