feat(vad): add Silero VAD and drop silence-only buffers (#447)

* feat(vad): replace amplitude-based VAD with Silero neural network

Replace the simple amplitude threshold VAD with Silero VAD, a lightweight
neural network model that classifies audio as speech/non-speech. This
addresses the root cause of #302 (silence not stopping recording) and

- Add silero_vad.py wrapper using ONNX Runtime with bundled Silero v5 model
- Accumulate 512-sample chunks with 64-sample context window per official API
- Map existing vad_sensitivity (1-5) to Silero thresholds (0.8-0.3)
- Use max() across sub-chunks to avoid missing speech onsets
- Fall back to amplitude VAD when onnxruntime is unavailable
- Add onnxruntime as optional dependency (pip install vocalinux[vad])

Closes #344

* address review: add tests, LICENSE, logging, validation fixes

- Add unit tests for SileroVAD (process, reset, fallback, sensitivity mapping)
- Add MIT LICENSE for bundled Silero VAD model in data/
- Log which VAD backend is active on init
- Validate chunk length in SileroVAD.process()
- Skip is_speech check until a full Silero chunk is processed
- Add thread safety note to SileroVAD docstring
- Document resampling rate effect on VAD resolution
- Comment explaining why load_silero_vad() catches broad Exception

* address review: bundle license, document [vad] extra, surface backend in UI

- Pack data/LICENSE into the wheel (pyproject package-data) so attribution
  travels with the model
- README: short note on enabling neural VAD via vocalinux[vad]
- Settings: VAD Sensitivity row subtitle shows the active backend; if
  onnxruntime is missing, an info-row beneath the group spells out the
  install command and the restart requirement
- silero_vad.is_silero_available() probes onnxruntime + model presence
  w/o instantiating an InferenceSession
- CI installs .[dev,vad] so Silero paths get exercised
- Integration test for _record_audio Silero branch (mocked pyaudio +
  scripted SileroVAD), covering silence flush, speech reset, and
  sensitivity threshold mapping at sens=1 vs sens=5
- Tests no longer skip when other modules globally mock numpy: pop the
  top-level numpy ref so a fresh import gives the real package, and
  swap sys.modules["numpy"] inside the _record_audio call so the lazy
  import inside the function picks up real numpy too

* fix(vad): drop silence-only recording buffers

* test(vad): align stop buffer expectations

* test(vad): preserve real numpy module

* fix(install): install vad support opportunistically

* test(vad): cover recognition manager vad edges

---------

Co-authored-by: Sbenazar <127324689+Sbenazar@users.noreply.github.com>

.github/workflows/unified-pipeline.yml

@@ -143,7 +143,7 @@ jobs:
           python -m pip install --upgrade pip setuptools wheel
           # Install PyGObject from pip (with build deps installed above)
           pip install PyGObject
-          pip install -e ".[dev]"
+          pip install -e ".[dev,vad]"
           echo "VIRTUAL_ENV=$VIRTUAL_ENV" >> $GITHUB_ENV
           echo "PATH=$VIRTUAL_ENV/bin:$PATH" >> $GITHUB_ENV