Add optional Xquik social evidence guidance

[kriptoburak]

Summary

• Adds optional Xquik evidence guidance to the Vantage social skill.
• Keeps web-only research as the default and skips Xquik when it is not configured.
• Requires citation details for public X posts, profiles, search results, and engagement snapshots.

Validation

• git diff --check
• frontmatter and section check
• confidentiality and auth-header scan
• changed files add no new links