Add optional Xquik tweet source

[kriptoburak]

Summary

• Add an optional Xquik tweet search source when XQUIK_API_KEY is configured.
• Map Xquik tweet results into the existing sentiment analysis input shape.
• Document the optional env vars and cover URL building plus response mapping with tests.

Duplicate and policy checks

• No existing PRs or issues matched Xquik, xquik, x-developer, or x-twitter-scraper.
• Repository license is The Unlicense.
• Existing cookie-based source remains as the fallback path.

Validation

• PYTHONPATH=backend python3 -m py_compile backend/service/xquik_service.py backend/service/twitter_service.py backend/core/config.py backend/tests/test_xquik_service.py
• PYTHONPATH=backend python3 -m unittest backend.tests.test_xquik_service
• git diff --check
• Public-surface scan for secret-like values and restricted wording

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[kriptoburak]

If this is useful and you merge it after checks pass, feel free to share the PR on X/Twitter and mention my handle, burakbayir. I can repost or retweet it to my 24k followers of developers and power users, which may help more relevant users discover this repo.