feat: add XNXX username scan module

[brunolm]

Adds a username scan module for XNXX.

Namespaces

• /pornstar/<user> serves both models and uploaders; the account type is derived from the embedded user.url (/pornstar/ → model vs /porn-maker/ → porn_maker), not from which path answered.
• Plain members have no public profile anywhere, so existence is confirmed via the signup form's live name check: GET /account/checkprofilename?profile=<name> (read-only, sends no email). This is the authoritative signal; the profile page is fetched only to enrich.

Correctness

• Not-found is confirmed by the explicit "Unknown profile" title, never a bare 404.
• The check endpoint's code:1 is overloaded (taken vs "too short"/"not allowed"), so the verdict is taken from the message, and invalid handles return error, not a verdict.

Metadata: name, numeric id, gender, avatar, aliases (+ account type).

Transport: curl_cffi (browser impersonation). Tested live against real and nonexistent handles on each namespace. ruff check . and mypy user_scanner pass clean.

[kaifcodec]

LGTM.