docs: add Hermes Tweet backend option

[kriptoburak]

Summary

• document Hermes Tweet as an optional Hermes Agent backend for X/Twitter workflows
• keep macli as the primary route for local macOS cookie, archive, and media tasks
• add the same install guidance to README.md and SKILL.md for agent discovery

Validation

• git diff --check
• conflict-marker scan clean
• added-line public-safe scan clean
• GitHub link checks passed for Hermes Agent, Hermes Tweet, and macos-cli