fix: bounce silent — AudioRoutingEngine no longer full-tears-down sink on dest change

stopAllPlayback->updateSfRouting->startTrackPlayback reroutes bridge sink
twice during bounce; each dest change previously called this.disconnect()
= BridgeAudioNode teardown + async worklet reload, audio swallowed into
_preBuffer (bounded 64 blocks) forever if worklet never reactivates ->
silent WAV (only old reverb tail). Fix: rely on BridgeAudioNode.connect()
re-pointing _gainNode (already handles dest switch without teardown);
init() only when not ready. Add __sfDiag ROUTE + BRIDGE_AUDIO (frames/
peak/path per sec) to verify at bounce end.

app/static/js/services/audioRoutingEngine.js

@@ -24,8 +24,8 @@
       // Idempotent: updateSfRouting/ensureMasteringRouting chay tren MOI keydown/
       // note-on — neu da noi dung dest thi KHONG disconnect (disconnect flush ring
       // -> am phim dang vang bi cat). Chi doi khi dest/track thuc su khac.
+      if (window.__sfDiag) window.__sfDiag("ROUTE to=" + (trackId || "masterBus") + " prev=" + (this._trackId || "masterBus") + " bridgeReady=" + bridgeNode.isReady() + " conn=" + this._connected);
       if (this._connected && this._dest === dest && this._trackId === (trackId || null)) return true;
-      this.disconnect();
       if (!bridgeNode.isReady()) bridgeNode.init();
       bridgeNode.connect(dest);
       this._connected = true;