docs: add Hermes Tweet public context

[kriptoburak]

Summary

• Add Hermes Tweet as an optional public-context companion for Hermes users.
• Keep xurl as Awaek's source of truth for private bookmark sync.
• Document the read-only boundary: XQUIK_API_KEY for reads and HERMES_TWEET_ENABLE_ACTIONS unset.

Notes

• GitHub did not report license metadata during review.

Validation

• git diff --check
• Added-line private term scan
• Added-line dash scan
• curl -fsSI https://github.com/Xquik-dev/hermes-tweet