Add optional Xquik Twitter backend

[kriptoburak]

Summary

• Add an opt-in Xquik backend for Twitter alerts through TWITTER_BACKEND=xquik.
• Keep the existing Tweepy path as the default backend.
• Reuse the current Twitter text cleanup for both Twitter and email output.

Validation

• python3 -m black config.py handler.py
• python3 -m py_compile config.py handler.py
• git diff --check
• curl https://xquik.com/api/v1/x/tweets returned 401, confirming the endpoint is reachable and requires authentication.