fix(a-app): gate modular MLP routing on example count to preserve default patch

Modular mode's default patch sets MM_Matrix/s00_d08_amp = 1.0 via
_setRawByLabel at engine init, but on the first inference tick
routeOutputs writes the untrained MLP's output (~0.5 normalised) to
every paramMeta index. For matrix cells the raw range is [-1, 1], so
normalised 0.5 denormalises to 0 — clobbering the default amp routing
and killing all audio.

Skip the setParam loop for modular when iml.exampleCount === 0, so the
worklet keeps running on the default patch we already pushed at init.
Once the user captures at least one training example the MLP has a
target to reproduce, and routing resumes normally.

Only affects modular mode; other engines are unchanged.

playground/js/a-app.js

@@ -2398,8 +2398,16 @@ function routeOutputs(outputs) {
       modularUI.updateLive(overridden);
     }
 
+    // Modular mode cold-start gate: with no training examples, an untrained
+    // MLP produces outputs around 0.5 which denormalise to ~0 for matrix
+    // cells (min=-1, max=1) and clobber the default patch's s00_d08_amp=1.0.
+    // Result: silence. Until the user captures at least one example, leave
+    // the worklet running on the default patch we already pushed at init.
+    const skipModularRouting = activeEngine?.id === 'modular' &&
+      (iml?.exampleCount ?? 0) === 0;
+
     // Engine param updates: throttle + dead-zone filter
-    if (activeEngine && activeEngine.running) {
+    if (activeEngine && activeEngine.running && !skipModularRouting) {
       const now = performance.now();
       if (now - _lastParamSendTime >= PARAM_SEND_INTERVAL) {
         _lastParamSendTime = now;