Add bounded CPU VAD diagnostic with real model contract tests

docs/ROADMAP.md

@@ -79,6 +79,9 @@ release. Keep their evidence and unchecked production gates intact.
   calibrated handling of queries without a relevant match.
   - [x] Prepare bounded CPU speech diagnostics and test process failures,
     timestamp units and frozen-label scoring; see [speech proposal](SPEECH-ALIGNMENT.md).
+  - [x] Build a pinned CPU VAD diagnostic with explicit one-thread inference,
+    native error detection and full probabilities; actual Silero silence/input
+    contracts passed. Media quality comparison remains open (see SPEECH-VAD.md).
   - [ ] Run genuine local speech candidates, Google transcript retrieval and
     held-out English/German/music/no-speech checks before selecting a default.
 - [ ] Package and verify decoders on every release OS; test production acceleration.