The previous fix fell back to the scheme's default port (443/80) when
url.port was empty, but url.port is empty for *both* 'wss://host:443'
and 'wss://host' — causing the validation to wrongly accept a URL with
no port at all.
Fix: inspect the raw authority segment of the URL string to check
whether a ':port' component is actually present, regardless of whether
that port is the scheme default.
Add gateway-form.test.ts covering:
- explicit non-default ports (accepted)
- explicit default ports :443 / :80 (accepted — regression case)
- missing port (rejected)
- wrong scheme (rejected)
- invalid URL (rejected)
- whitespace trimming
Closes#148
