fix: collapse repeated whitespace in usernames

[Prajjwaltripathi20]

Fixes issue #27 by improving username normalization to collapse repeated whitespace into a single separator.

Changes

• Trim leading and trailing whitespace.
• Convert usernames to lowercase.
• Replace consecutive whitespace with a single hyphen.

Verification

• John Smith → john-smith
• Alice Cooper → alice-cooper
• Bob → bob

Fixes #27

[Prajjwaltripathi20]

I've submitted a PR that fixes this issue by collapsing repeated whitespace during username normalization.