Add an optional Caddy service (proxy profile) to compose.prod.yaml for
automatic HTTPS on a custom domain, with a Caddyfile that transparently
proxies WebSocket upgrades.
Move Echo setup into resources/js/echo.ts and derive the Reverb host from
window.location when VITE_REVERB_* is unset, so the published image's frontend
connects on any domain without a rebuild. The release workflow bakes a fixed
public Reverb key and leaves host/port/scheme empty to enable this; the Herd
dev setup keeps its explicit VITE_REVERB_* values, so its behaviour is
unchanged.
Drop the now-unneeded 8080 host port — the WebSocket rides the main HTTP(S)
port via the in-container nginx /app proxy.
