feat(onnx-asr): реализовать ensure_model_available

- Зачем:
  - Бэкенд должен резолвить алиасы моделей и сохранять compute_type для дальнейшего использования.
- Что:
  - добавлен конструктор __init__ с полями actual_compute_type, _resolved_model_id, _vad.
  - метод ensure_model_available валидирует алиас и возвращает идентификатор модели onnx-asr.
  - написаны 3 теста на резолвинг и сохранение compute_type.
- Проверка:
  - uv run pytest tests/test_onnx_asr.py -v

src/local_transcriber/backends/onnx_asr.py

@@ -2,6 +2,9 @@
 
 from __future__ import annotations
 
+from collections.abc import Callable
+from typing import Any
+
 MODEL_ALIASES: dict[str, str] = {
     "gigaam-v3": "gigaam-v3-ctc",
     "parakeet-v3": "nemo-parakeet-tdt-0.6b-v3",
@@ -13,6 +16,26 @@ SUPPORTED_ALIASES = ", ".join(MODEL_ALIASES)
 class OnnxAsrBackend:
     """Бэкенд транскрипции через onnx-asr (ONNX Runtime)."""
 
+    def __init__(self):
+        self.actual_compute_type: str | None = None
+        self._resolved_model_id: str | None = None
+        self._vad: Any = None
+
+    def ensure_model_available(
+        self,
+        model_name: str,
+        compute_type: str,
+        on_status: Callable[[str], None] | None = None,
+    ) -> str:
+        """Resolves model alias and returns the onnx-asr model identifier.
+
+        onnx-asr downloads models automatically via load_model(),
+        so this just validates the alias and returns the identifier string.
+        """
+        self.actual_compute_type = compute_type
+        self._resolved_model_id = self._resolve_model(model_name)
+        return self._resolved_model_id
+
     def _resolve_model(self, model_name: str) -> str:
         """Resolve alias to onnx-asr model name. Raw names pass through."""
         if model_name in MODEL_ALIASES:

tests/test_onnx_asr.py

@@ -4,6 +4,24 @@ import pytest
 from local_transcriber.backends.onnx_asr import OnnxAsrBackend, MODEL_ALIASES
 
 
+class TestEnsureModelAvailable:
+    def test_returns_model_id_for_gigaam(self):
+        backend = OnnxAsrBackend()
+        result = backend.ensure_model_available("gigaam-v3", "int8")
+        assert result == "gigaam-v3-ctc"
+
+    def test_returns_model_id_for_parakeet(self):
+        backend = OnnxAsrBackend()
+        result = backend.ensure_model_available("parakeet-v3", "fp16")
+        assert result == "nemo-parakeet-tdt-0.6b-v3"
+
+    def test_stores_compute_type(self):
+        backend = OnnxAsrBackend()
+        backend.ensure_model_available("gigaam-v3", "float32")
+        assert backend._resolved_model_id == "gigaam-v3-ctc"
+        assert backend.actual_compute_type == "float32"
+
+
 class TestModelAliases:
     def test_gigaam_v3_resolves(self):
         backend = OnnxAsrBackend()