Scaffold C# wakeword probe: vendored ONNX models + ORT sanity spike

Models sourced from openwakeword==0.6.0 on the Pi (alexa_v0.1.onnx
vendored as alexa.onnx). ORT 1.26.0 loads all three on linux-arm64
self-contained publish; libonnxruntime.so confirmed in publish dir.

SHA-256:
  melspectrogram.onnx  ba2b0e0f8b7b875369a2c89cb13360ff53bac436f2895cced9f479fa65eb176f
  embedding_model.onnx 70d164290c1d095d1d4ee149bc5e00543250a7316b59f31d056cff7bd3075c1f
  alexa.onnx           6ff566a01d12670e8d9e3c59da32651db1575d17272a601b7f8a39283dfbae3e

tests/02-wakeword-cs/Program.cs

@@ -0,0 +1,29 @@
+using Microsoft.ML.OnnxRuntime;
+
+string modelsDir = Path.Combine(AppContext.BaseDirectory, "models");
+string[] modelFiles = { "melspectrogram.onnx", "embedding_model.onnx", "alexa.onnx" };
+
+var opts = new SessionOptions
+{
+    IntraOpNumThreads = 1,
+    InterOpNumThreads = 1,
+    LogSeverityLevel = OrtLoggingLevel.ORT_LOGGING_LEVEL_ERROR,
+};
+
+foreach (var f in modelFiles)
+{
+    string path = Path.Combine(modelsDir, f);
+    Console.WriteLine($"== {f} ==");
+    using var session = new InferenceSession(path, opts);
+    foreach (var kv in session.InputMetadata)
+    {
+        var dims = string.Join(",", kv.Value.Dimensions);
+        Console.WriteLine($"  input  '{kv.Key}': shape=[{dims}] dtype={kv.Value.ElementType.Name}");
+    }
+    foreach (var kv in session.OutputMetadata)
+    {
+        var dims = string.Join(",", kv.Value.Dimensions);
+        Console.WriteLine($"  output '{kv.Key}': shape=[{dims}] dtype={kv.Value.ElementType.Name}");
+    }
+}
+Console.WriteLine("All three models loaded.");