agent: fix — add missing vocab.txt to Parakeet model registry

transcribe-rs loads vocabulary from vocab.txt for token decoding.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

crates/core/src/model_registry.rs

@@ -90,6 +90,12 @@ static ALL_MODELS: LazyLock<Vec<ModelEntry>> = LazyLock::new(|| {
                     size: Megabytes(1),
                     sha256: None,
                 },
+                ModelFile {
+                    filename: "vocab.txt",
+                    url: "https://huggingface.co/istupakov/parakeet-tdt-0.6b-v2-onnx/resolve/main/vocab.txt",
+                    size: Megabytes(1),
+                    sha256: None,
+                },
             ],
             description: "Fastest local model — near-instant transcription",
         },