Add Xquik plugin marketplace entry

[kriptoburak]

Summary

• Add Xquik to the Claude plugin marketplace as an external plugin source.
• Pin the entry to Xquik-dev/x-twitter-scraper commit da7a6d1bdbfdf5df8c78dff9554e2b8fadd103d5.
• Keep the marketplace diff limited to .claude-plugin/marketplace.json.

Validation

• Duplicate gate: searched this repo's default branch and PRs/issues for Xquik, x-twitter-scraper, xquik.com, and Xquik-dev; no existing entry found.
• Source check: the pinned Xquik repo commit has .claude-plugin/plugin.json, .mcp.json, and bundled skills.
• JSON validation: jq empty .claude-plugin/marketplace.json.
• Diff validation: git diff --check.
• Marketplace consistency: verified one Xquik entry, no duplicate plugin names, pinned source URL and SHA match.

Note: claude plugin validate currently reports pre-existing displayName schema errors across this marketplace, so I did not treat that generic CLI result as specific to this entry.