docs: add Hermes Tweet backend option

[kriptoburak]

Summary

• Document Hermes Tweet as an optional Hermes Agent backend for API-key-backed X/Twitter workflows.
• Keep xpost as the direct OAuth/API v2 path.
• Make Hermes write actions explicit and gated behind HERMES_TWEET_ENABLE_ACTIONS=true.

Validation

• git diff --check
• Conflict-marker scan on README.md and SKILL.md
• Added-line public-safety scan for private provider or secret-bearing terms
• Direct HEAD checks for the Hermes Tweet and xpost GitHub links

[chatgpt-codex-connector]

You have reached your Codex usage limits for code reviews. You can see your limits in the Codex usage dashboard.
To continue using code reviews, add credits to your account and enable them for code reviews in your settings.