fix(vad): bundle local Silero model

[问题原因]
- 先前实现会在包内权重缺失时读取外部 faster-whisper 资源，无法满足自包含部署要求。

[问题根因]
- 项目包中尚未包含已验证的 ONNX 权重，VAD 路径保留了开发期回退逻辑。

[修复方案]
- 提交已校验 SHA-256 的本地 Silero ONNX 权重并移除外部包回退。
- 增加模型打包和缺失模型失败路径测试，并更新来源、MIT 许可和哈希说明。

[影响范围]
- VAD 现在只加载项目包内模型，不联网且不依赖 faster-whisper 运行时资源。
- 未安装、启用或启动任何用户 systemd 服务。

5 files changed, 30 insertions, 16 deletions

diff --git a/README.md b/README.md
index 95a13f7..ce8c844 100644
--- a/README.md
+++ b/README.md
@@ -30,7 +30,7 @@
 src/mic_clipper/assets/silero_vad_v6.onnx
 ```
 
-该权重应从当前机器已验证的 `faster-whisper` 1.2.1 本地资源复制而来，归属和 MIT 许可说明见 [THIRD_PARTY_NOTICES.md](THIRD_PARTY_NOTICES.md)。当前开发代码为便于本机测试会回退读取该已预置的本地资源；它不会下载模型。该回退不是自包含部署方案，审阅/部署前必须把权重复制进项目包。
+该权重已从当前机器已验证的 `faster-whisper` 1.2.1 本地资源复制进项目包。归属、MIT 许可声明和 SHA-256 校验值见 [THIRD_PARTY_NOTICES.md](THIRD_PARTY_NOTICES.md)。运行时代码只读取包内模型；不会下载模型，也不会回退读取外部包资源。
 
 ## 安装与服务
 
diff --git a/THIRD_PARTY_NOTICES.md b/THIRD_PARTY_NOTICES.md
index e38fc8e..e147b4e 100644
--- a/THIRD_PARTY_NOTICES.md
+++ b/THIRD_PARTY_NOTICES.md
@@ -2,12 +2,14 @@
 
 ## Silero VAD ONNX weight
 
-The intended bundled file is `src/mic_clipper/assets/silero_vad_v6.onnx`.
+The bundled file is `src/mic_clipper/assets/silero_vad_v6.onnx`.
 
-Its local source is the `assets/silero_vad_v6.onnx` file in the verified
-`faster-whisper` 1.2.1 installation. That package's installed metadata declares
-the MIT license and its VAD implementation attributes the model integration to
+It was copied from `assets/silero_vad_v6.onnx` in the locally verified
+`faster-whisper` 1.2.1 installation. Both files have SHA-256
+`4cbf549b8326f60f80f2536d9eefeb450a9abe83365a098031c89719f1be17d2`.
+The installed package metadata declares the MIT license, and its VAD
+implementation attributes the model integration to
 [`snakers4/silero-vad`](https://github.com/snakers4/silero-vad).
 
-The ONNX weight has no network retrieval path in this project. The asset must be
-present before deployment; it is intentionally not downloaded at runtime.
+The ONNX weight is bundled and has no network retrieval path. The application
+never downloads models at runtime.
diff --git a/src/mic_clipper/assets/silero_vad_v6.onnx b/src/mic_clipper/assets/silero_vad_v6.onnx
new file mode 100644
index 0000000..9febab9
--- /dev/null
+++ b/src/mic_clipper/assets/silero_vad_v6.onnx
diff --git a/src/mic_clipper/vad.py b/src/mic_clipper/vad.py
index 705dfd8..e82d15a 100644
--- a/src/mic_clipper/vad.py
+++ b/src/mic_clipper/vad.py
@@ -47,13 +47,8 @@ class SileroVad:
     @staticmethod
     def _default_model_path() -> Path:
         bundled = resources.files("mic_clipper.assets").joinpath("silero_vad_v6.onnx")
-        if bundled.is_file():
-            return Path(bundled)
-        try:
-            import faster_whisper
-        except ImportError as error:
+        if not bundled.is_file():
             raise RuntimeError(
-                "Silero VAD model is missing; bundle silero_vad_v6.onnx or install the "
-                "pre-provisioned faster-whisper runtime asset"
-            ) from error
-        return Path(faster_whisper.__file__).parent / "assets" / "silero_vad_v6.onnx"
+                "packaged Silero VAD model is missing: silero_vad_v6.onnx"
+            )
+        return Path(bundled)
diff --git a/tests/test_vad.py b/tests/test_vad.py
index 98826ae..f2e3d65 100644
--- a/tests/test_vad.py
+++ b/tests/test_vad.py
@@ -1,6 +1,8 @@
 import numpy as np
 import pytest
+from importlib import resources
 
+import mic_clipper.vad as vad_module
 from mic_clipper.vad import FRAME_SAMPLES, SileroVad
 
 
@@ -12,6 +14,21 @@ def test_bundled_silero_vad_accepts_512_samples_and_returns_probability():
     assert 0.0 <= probability <= 1.0
 
 
+def test_silero_weight_is_packaged_with_the_application():
+    model_path = resources.files("mic_clipper.assets").joinpath("silero_vad_v6.onnx")
+
+    assert model_path.is_file()
+
+
+def test_missing_packaged_weight_does_not_fall_back_to_an_external_package(
+    monkeypatch, tmp_path
+):
+    monkeypatch.setattr(vad_module.resources, "files", lambda _package: tmp_path)
+
+    with pytest.raises(RuntimeError, match="packaged Silero VAD model is missing"):
+        SileroVad._default_model_path()
+
+
 def test_bundled_silero_vad_rejects_non_512_sample_frames():
     vad = SileroVad()