Auris v1.2.0

Add energy-based VAD with high-pass filter

Introduce an energy-based voice activity detector to reduce spurious transcriptions on silence/noise. Adds vad_thold and freq_thold config options (defaults: 0.6 and 100 Hz) to Lua configs and exposes them via the Lua API. Implements auris::vad_simple (vendored from whisper.cpp examples) in new source/vad.{cpp,h}, applies an optional high-pass filter before VAD, and wires the gate into the WorkerLoop to skip low-energy chunks. Defaults and behavior: tail energy compared against whole-chunk average; set vad_thold <= 0 to disable VAD, set freq_thold = 0 to disable filtering.