fix: record at 48000 Hz — PipeWire virtual sinks reject 16 kHz resampling

Whisper and faster-whisper both handle arbitrary sample rates internally.

audio.py

@@ -4,7 +4,7 @@ import numpy as np
 
 
 class AudioRecorder:
-    def __init__(self, sample_rate: int = 16000, device: str | None = None):
+    def __init__(self, sample_rate: int = 48000, device: str | None = None):
         self.sample_rate = sample_rate
         self.device = device or None
         self._buffer: list[np.ndarray] = []