Add Xquik product signal skill

[kriptoburak]

Summary

Adds xquik-product-signal-research, a read-only skill that combines JoomPulse product context with Xquik public X search, trends, monitors, and extraction workflows for product signal research.

Updates the README skills table with the new workflow.

Public-Safety Checklist

• No credentials, tokens, keys, or secrets.
• No internal filesystem paths.
• No private Slack, Jira, Notion, admin, or service URLs.
• No private service names or implementation details.
• No customer data or private product data.
• Skill directory name matches SKILL.md frontmatter name.

Validation

• bash scripts/check-public-safety.sh
• Skill frontmatter validation for all skills/*/SKILL.md files
• git diff --cached --check
• Staged diff scan for em dash, local paths, and sensitive wording markers
• Link checks: https://docs.xquik.com, https://docs.xquik.com/mcp/overview, and https://xquik.com/openapi.json returned HTTP 200

Duplicate Check

Checked memory, target tree, all-state pull requests, and all-state issues for Xquik, x-twitter-scraper, Twitter, and product signal terms. No duplicate target route was found.