docs: add optional Xquik path to x-api skill

[kriptoburak]

What Changed

• Added an optional Xquik REST and remote MCP path to the existing x-api skill.
• Kept direct X API examples as the default path.
• Updated the x-api skill prompt metadata so the optional route is discoverable.

Why This Change

EOC's x-api skill already covers X posting, timelines, search, and analytics. Xquik has public docs, an OpenAPI spec, and an authenticated remote MCP endpoint, so this adds a source-backed opt-in path for users who already choose Xquik.

Testing Done

• Manual testing completed
• Automated tests pass locally (node tests/run-all.js)
• Edge cases considered and tested

Focused validation:

• node scripts/ci/validate-skills.js
• npm run catalog:check
• node scripts/ci/check-unicode-safety.js
• git diff --check
• Link checks: docs overview, OpenAPI, and server card returned 200; remote MCP returned an auth challenge as expected.

Type of Change

• fix: Bug fix
• feat: New feature
• refactor: Code refactoring
• docs: Documentation
• test: Tests
• chore: Maintenance/tooling
• ci: CI/CD changes

Security & Quality Checklist

• No secrets or API keys committed (ghp_, sk-, AKIA, xoxb, xoxp patterns checked)
• JSON files validate cleanly (no JSON files changed)
• Shell scripts pass shellcheck (if applicable, no shell scripts changed)
• Pre-commit hooks pass locally (if configured)
• No sensitive data exposed in logs or output
• Follows conventional commits format

Documentation

• Updated relevant documentation
• Added comments for complex logic (not applicable, no code logic changed)
• README updated (not needed)