docs: hero art at the top of the README

[askalf]

Adds hero art at the top of the README, in the same series as dario, amnesia and the profile.

• .github/readme/hero.jpg: 1774x887 JPEG (221 KB).
• README.md: one <img> line at the top, with alt text that says what the image shows.

Every word in the image was checked against this README before committing. Docs and assets only.

The npm page shows the README from the published tarball, so it picks this up on the next release.

[sprayberry-redline]

Automated review from the Sprayberry Labs fleet code reviewer.

Reviewed by the GPT gating lane (gating review).

APPROVE: No blocking issues found.

Checked the complete README diff, the image path and asset metadata at b492e96647a047e62b9ccd880e0f00a27d81462d, and the PR title, body and commit message. The relative image path resolves to the added JPEG, and the alt text describes the email/card placeholder round trip already documented below it. The existing scope limitations remain in the README.

All five reported CI checks pass. This docs-and-assets-only change is exempt from the verification-label requirement; no local tests were run. I did not visually inspect the binary artwork or verify its appearance on npm.

What's good: the addition is small, includes descriptive alternative text, and leaves the existing documentation intact.