Add Xquik plugin

[kriptoburak]

Summary

• Add an Xquik Claude plugin with one workflow skill for X/Twitter data tasks.
• Register the plugin in the marketplace manifest and README plugin table.
• Update the README skill total and installation list.

Validation

• Checked the target tree, PRs, and issues for existing Xquik entries before pushing.
• Parsed the marketplace and plugin manifests as JSON.
• Verified README plugin and skill counts.
• Ran Git whitespace checks.
• Scanned the public diff for credentials, private implementation wording, badges, and unsupported claims.
• Checked referenced Xquik public links returned HTTP 200.

[kriptoburak]

Rebased the contribution onto the current main and resolved the marketplace conflict while preserving the newly added pi plugin. I also reconciled the README with the repository tree: all 11 plugins and all 53 skills, including the four existing skills that were missing from the index, are now represented.

Validated signed head a7146a8 by parsing every manifest, checking unique and matching plugin registrations, comparing all skill files against README rows and totals, checking all public references, scanning for conflict markers and credential patterns, running git diff --check, and running claude plugin validate . (passes; its 11 author-attribution warnings apply uniformly to every existing plugin).