ESP32 devices can't spare the 40KB+ RAM a TLS client needs, so Firebase
Storage's HTTPS-only download URLs were blocking melody downloads. Binaries
are now written to local disk (./data/melody_binaries) and served through a
new unauthenticated /api/melodies/download/{pid} route, exposed publicly on
a separate melodies.bellsystems.net vhost (plain HTTP, no TLS) so the main
console domain can stay HTTPS-only with no exceptions. Preview audio still
uses Firebase Storage since it's only ever fetched by the HTTPS admin UI.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
