Add public social and publishing skills

[MengTo]

What changed

• add publish-project-to-github
• add the platform-neutral prepare-social-post-launch
• add prepare-x-crosspost-drafts without an unpublished companion dependency
• update write-like-meng-on-x from 40 to 142 deduplicated authored posts and refresh its portable voice references

Why

These are the approved reusable, public-safe skills from the latest Codex skill audit. Skills explicitly listed in the local private registry are excluded.

Checks

• quick_validate.py passed for all four skills
• agents/openai.yaml prompts and description lengths validated
• Bash syntax passed for the GitHub audit script
• Python parsing passed for the social export inspector
• the X corpus check passed with 142 posts and zero duplicate IDs, URLs, or text hashes
• privacy and private-skill scans passed
• git diff --check passed