A contact list was exported from an old app. Each line should hold a name and an email, separated by a comma, but everything is messy.
Task: write clean_contacts(lines) that returns a list of tidy contacts, each in the form "Name <email>".
For each line:
- Split it at the first comma only. The part before is the name, the part after is the email.
- Name: remove whitespace at the ends, use exactly one space between words, and capitalise the first letter of each word (the rest lowercase).
- Email: remove whitespace at the ends and make it all lowercase.
- Skip any line that has no comma at all.
- Skip any line where the name or the email is empty after cleaning.
Keep the contacts in their original order. An empty list gives [].