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/bridgeAudioNode.js

@@ -101,6 +101,16 @@
   function onAudio(l, r) {
     if (!_initialized) init();
     var blk = { l: new Float32Array(l), r: new Float32Array(r) };
+    _frames = (_frames || 0) + blk.l.length;
+    for (var _i = 0; _i < blk.l.length; _i++) {
+      var _a = Math.abs(blk.l[_i]); if (_a > (_peak || 0)) _peak = _a;
+      var _b = Math.abs(blk.r[_i]); if (_b > (_peak || 0)) _peak = _b;
+    }
+    if (!_lastDiag || Date.now() - _lastDiag >= 1000) {
+      _lastDiag = Date.now();
+      if (window.__sfDiag) window.__sfDiag("BRIDGE_AUDIO frames=" + _frames + " peak=" + (_peak ? (20 * Math.log10(_peak)).toFixed(1) : "-inf") + "dB path=" + (_useWorklet ? "worklet" : (_preBuffer.length ? "preBuffer" : "chunks")));
+      _peak = 0;
+    }
     if (_useWorklet && _workletNode) {
       _workletNode.port.postMessage({ type: 'audio', l: blk.l, r: blk.r });
       return;