Caddy `templates` only processes text/html + text/plain by default, so the
text/javascript env.js was served with {{env "API_BASE"}} unevaluated (a literal
that's also a JS parse error). Name the JS MIME types in the templates directive
so the API_BASE injection works — required for prod to point at the prod API
(staging worked only via the index.html fallback).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>