Add X social approval skill template

[kriptoburak]

Summary

Add a reusable x-social-approval skill template for approval-gated X/Twitter and social-media workflows.

Linked Issue

None. This is a narrowly scoped reusable skill contribution, which CONTRIBUTING.md allows to go directly to a focused PR.

What Changed

• Adds skill_template/x_social_approval/SKILL.md.
• Updates the Quick Start example so users who install skill_template/ can try x-social-approval as an available skill name.

Testing

• python3 /tmp/anthropics-skills-tweetclaw-161004/skills/skill-creator/scripts/quick_validate.py skill_template/x_social_approval
• Frontmatter description length and angle-bracket checks
• git diff --check

Checklist

• I read CONTRIBUTING.md
• For a new feature or behavior change, I opened or linked an issue first, or kept the change to a small reusable skill contribution
• I kept the change focused and updated docs or examples if needed
• I ran relevant tests or examples, or explained why I did not