feat(recorder): add offline voice clip pipeline

[变更性质]
- 本提交新增本机离线的语音片段录音能力，不涉及网络服务或语音识别。

[新增功能]
- 通过 Pulse 默认输入持续采集音频，以本地 Silero VAD 触发片段。
- 以私有目录和权限写入 24 kbps Ogg/Opus 录音，并提供 systemd 用户服务安装器。

[实现方案]
- 使用有限前置缓冲、静音封段和最长段滚动状态机，避免静音落盘及内存无限增长。
- 增加真实 Opus 编解码、服务 dry-run 和纯逻辑状态转换测试；记录模型归属和部署前置条件。

[影响范围]
- 新增 Python CLI、运行时模块、中文运维文档和自动测试。
- 未安装、启用或启动任何用户 systemd 服务；不删除或修改录音数据。

1 files changed, 72 insertions, 0 deletions

diff --git a/src/mic_clipper/audio_input.py b/src/mic_clipper/audio_input.py
new file mode 100644
index 0000000..1d77aa0
--- /dev/null
+++ b/src/mic_clipper/audio_input.py
@@ -0,0 +1,72 @@
+"""PipeWire/Pulse microphone capture through the local ffmpeg binary."""
+
+from __future__ import annotations
+
+import subprocess
+from collections.abc import Iterator
+
+import numpy as np
+
+from mic_clipper.vad import FRAME_SAMPLES
+
+
+class AudioInputUnavailable(RuntimeError):
+    """The dynamic Pulse default source could not supply another frame."""
+
+
+class PulseAudioInput:
+    """Yield fixed 16 kHz mono float PCM frames from Pulse's `default` source."""
+
+    @staticmethod
+    def command() -> list[str]:
+        return [
+            "ffmpeg",
+            "-nostdin",
+            "-hide_banner",
+            "-loglevel",
+            "error",
+            "-f",
+            "pulse",
+            "-sample_rate",
+            "16000",
+            "-channels",
+            "1",
+            "-i",
+            "default",
+            "-ac",
+            "1",
+            "-ar",
+            "16000",
+            "-f",
+            "f32le",
+            "pipe:1",
+        ]
+
+    def frames(self) -> Iterator[np.ndarray]:
+        process = subprocess.Popen(
+            self.command(),
+            stdin=subprocess.DEVNULL,
+            stdout=subprocess.PIPE,
+            stderr=subprocess.PIPE,
+        )
+        assert process.stdout is not None
+        assert process.stderr is not None
+        try:
+            while True:
+                payload = process.stdout.read(FRAME_SAMPLES * np.dtype("<f4").itemsize)
+                if len(payload) != FRAME_SAMPLES * np.dtype("<f4").itemsize:
+                    error = process.stderr.read(4096).decode("utf-8", errors="replace").strip()
+                    return_code = process.wait()
+                    detail = f": {error}" if error else ""
+                    raise AudioInputUnavailable(
+                        f"ffmpeg Pulse input ended with exit code {return_code}{detail}"
+                    )
+                yield np.frombuffer(payload, dtype="<f4").copy()
+        finally:
+            if process.poll() is None:
+                process.terminate()
+                try:
+                    process.wait(timeout=5)
+                except subprocess.TimeoutExpired:
+                    process.kill()
+                    process.wait()