Header names arrive lowercase over HTTP/2 (the nginx front end enables
it) and Apache preserves that case, so the X-GitHub-Event lookup missed
and every email reported "Unknown". Normalise header keys once.
- docs.htm: dark single-page redesign in plain CSS, live URL builder,
all four parsers documented, Bootstrap CDN dependency dropped
- index.php: respond with pretty-printed JSON (success and 400 error);
email "Parsed Variables" block uses JSON instead of print_r
- parsers/helpers.php: emailShell() provides one stylesheet, header and
footer for every email template; five duplicated stylesheets removed
Andy Dixon