Add Lobsters (lobste.rs) and Codepen username availability module

[SpiliosDimakopoulos]

Adds a username availability check for Lobsters (lobste.rs), a tech/OSINT community site currently missing from user_scan/community/.

• File: user_scanner/user_scan/community/lobsters.py
• Uses the public, documented JSON endpoint lobste.rs/u/.json
• Available: HTTP 404
• Taken: HTTP 200 + parsed JSON, extracts about/karma/created_at/github_username when present
• Error: any other status code or unparseable body

Tested locally against a known existing username and a random non-existent one; both paths resolve correctly.

[kaifcodec]

@SpiliosDimakopoulos Could you check if the response payload contains any other explicit strings like "user doesn't exist" or "profile not found"? We could use a targeted check like:

if response.status_code == 404 and "profile not found" in response.text:

this removes the risk of any false negatives in future.

[kaifcodec]

@SpiliosDimakopoulos Another issue I noticed is that the CodePen module is returning a 403 status code on my machine. This could be due to WAF restrictions that require custom headers, cookies, or updated request handling. Could you re-test this module on your end and verify if it requires updated headers?