fix(calls): DTLN at 16kHz + raw-capture A/B; explains weak/robotic results

Two issues found from real testing of the in-app tester:

1. Raw ≈ RNNoise ≈ Speex sounded identical in Record & compare because the clip
   was captured with browser noise suppression ON (the user's native-NS
   setting), so "Raw" was already cleaned and the models had nothing left to
   remove. Record & compare now captures fully raw audio (noiseSuppression /
   AGC / echoCancellation off) so each model's effect on real noise is audible.
   (Friends still heard differences in calls — the models work; the test was
   feeding them pre-cleaned audio.)

2. DTLN was robotic/choppy/quiet because @workadventure/noise-suppression
   targets 16 kHz (AUDIO_CONFIG.sampleRate) and does NOT resample internally,
   while we ran it at 48 kHz. Run DTLN's whole graph in a 16 kHz context:
   - denoisePipeline: add sampleRateFor(model) (16k for dtln, 48k otherwise);
     tester live-monitor + playback contexts use it (bufferSource resamples the
     48k clip down for DTLN).
   - shim (build/lotus-denoise.js): SAMPLE_RATE is now model-aware, so DTLN is
     correct in real calls too (it was previously broken at 48 kHz). The 16 kHz
     processed track is still published to LiveKit (WebRTC/Opus resamples).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

build/lotus-denoise.js

@@ -35,9 +35,13 @@
   if (typeof AudioWorkletNode === 'undefined' || typeof AudioContext === 'undefined') return;
 
   var ASSET_BASE = './denoise/';
-  var SAMPLE_RATE = 48000;
 
   var MODEL = params.get('lotusModel') || 'rnnoise';
+  // DTLN (@workadventure) targets 16 kHz and does not resample internally, so
+  // its whole graph runs in a 16 kHz context; RNNoise/Speex (sapphi) need
+  // 48 kHz. The processed MediaStreamTrack is published to LiveKit either way
+  // (WebRTC/Opus resamples as needed).
+  var SAMPLE_RATE = MODEL === 'dtln' ? 16000 : 48000;
   var USE_NATIVE_NS = params.get('lotusNativeNS') === 'true';
   var USE_GATE = params.get('lotusGate') === 'true';
   var GATE_THRESHOLD = parseFloat(params.get('lotusGateThreshold') || '-45');