Feature: Play remote audio on iPhone via WebAudio + self-hosted Opus WASM

iOS WebKit lacks Media Source Extensions with WebM/Opus, so remote audio
was silent on iPhone Safari/Chrome even though audio frames kept flowing.
Add a Web Audio API fallback path that decodes Opus packets with the
`opus-decoder` WASM library and schedules them onto an AudioContext.

The decoder bundle is now self-hosted — served at /static/opus-decoder.min.js
by both the Go and C++ servers — instead of pulled from a CDN, which was
unreachable from some networks.

Gotcha fixed during bring-up: the unscoped `opus-decoder` build's
`OpusDecoder.decodeFrame` is synchronous and returns {channelData,
samplesDecoded, sampleRate, errors} directly, not a Promise, so it must be
called in try/catch rather than via .then().

Also remove the on-screen diagnostic overlay (audio toast + frame counter)
used while debugging the phone without a console; diagnostics now go to
console.* only.

Co-Authored-By: deepseek-v4-pro

server/go/web/server.go

@@ -102,6 +102,7 @@ func (s *Server) Start() error {
 	mux.HandleFunc("/static/xterm.js", staticHandler(xtermJS, "application/javascript; charset=utf-8"))
 	mux.HandleFunc("/static/xterm.css", staticHandler(xtermCSS, "text/css; charset=utf-8"))
 	mux.HandleFunc("/static/xterm-fit.js", staticHandler(xtermFitJS, "application/javascript; charset=utf-8"))
+	mux.HandleFunc("/static/opus-decoder.min.js", staticHandler(opusDecoderJS, "application/javascript; charset=utf-8"))
 
 	s.srv = &http.Server{
 		Addr:              ":" + strconv.Itoa(s.port),