Rework PR #15 per security review SEC-14-R1: the client no longer carries
an API token. js/newsletter-config.js ships only the non-secret endpoint,
enforced https-only at config load time via validateEndpoint() (mirroring
the protocol allowlist in js/reading-list.js); js/newsletter.js POSTs
email-only with no Authorization header. Failure paths keep the single
user-safe message that never leaks token, endpoint, status, or raw body;
success still shows the confirmation. CI gains a gitleaks step that fails
on any secret hit; README documents the server-side token, the residual
signup-abuse risk, and the authoritative server-side validation follow-up.
Adds newsletter.html with an email signup form that POSTs to a configured
serverless endpoint. The endpoint and API token live in
js/newsletter-config.js (token defaults to an empty deploy-time placeholder,
never hardcoded in page logic). Missing/invalid tokens and network failures
surface a fixed user-safe error; successful signups show a confirmation.
Links the page from the site navigation on all pages.
implementer