Add Xquik to global API list

[kriptoburak]

Summary

• Add Xquik to the global Social API list.
• Link directly to the API reference.
• Use Unknown for CORS because the public docs do not state a broad browser CORS policy.

Checks

• Confirmed no existing Xquik entry or open duplicate PR/issue.
• Checked CONTRIBUTING.md format and placed the API at the bottom of the Social section.
• Ran git diff check.