WakewordModel: print shapes at startup + tidy mel-shape comment

Add PrintShapes() helper that writes input/output name, shape, and dtype
for each InferenceSession to stderr at construction time, prefixed with
[wakeword-model]. Called after each of the three session creations so the
geometry is visible on first run without grep-ing logs.

Also rephrase the stale "FIXED:" comment on the mel Dimensions[2] indexing
to plain explanatory text that describes the current invariant.

tests/02-wakeword-cs/WakewordModel.cs

@@ -59,8 +59,11 @@ internal sealed class WakewordModel : IDisposable
         };
 
         _mel = new InferenceSession(melPath, opts);
+        PrintShapes(Path.GetFileName(melPath), _mel);
         _emb = new InferenceSession(embeddingPath, opts);
+        PrintShapes(Path.GetFileName(embeddingPath), _emb);
         _cls = new InferenceSession(classifierPath, opts);
+        PrintShapes(Path.GetFileName(classifierPath), _cls);
 
         // Discover input names + assert shape geometry.
         _melInputName = _mel.InputMetadata.Keys.Single();
@@ -70,6 +73,17 @@ internal sealed class WakewordModel : IDisposable
         AssertClassifierShape(_cls);  // [batch, 16, 96], dtype float
     }
 
+    private static void PrintShapes(string filename, InferenceSession sess)
+    {
+        Console.Error.WriteLine($"[wakeword-model] {filename}");
+        foreach (var kv in sess.InputMetadata)
+            Console.Error.WriteLine(
+                $"  input  '{kv.Key}': shape=[{string.Join(",", kv.Value.Dimensions)}] dtype={kv.Value.ElementType.Name}");
+        foreach (var kv in sess.OutputMetadata)
+            Console.Error.WriteLine(
+                $"  output '{kv.Key}': shape=[{string.Join(",", kv.Value.Dimensions)}] dtype={kv.Value.ElementType.Name}");
+    }
+
     private static void AssertEmbeddingShape(InferenceSession sess)
     {
         if (!sess.InputMetadata.TryGetValue(EmbeddingInputName, out var meta))
@@ -144,7 +158,7 @@ internal sealed class WakewordModel : IDisposable
         var melOut = melResults.First().AsTensor<float>(); // shape (1, 1, n_frames, 32)
 
         // Apply openwakeword's `x / 10 + 2` transform and append each new frame to _melRing.
-        // FIXED: actual mel output shape is (1, 1, n_frames, 32) — n_frames is at Dimensions[2], NOT [1].
+        // Mel output shape is (1, 1, n_frames, 32). Note n_frames is at Dimensions[2], not [1].
         int nFrames = melOut.Dimensions[2];
         for (int f = 0; f < nFrames; f++)
         {