Add DMR digital voice, WebSDR, and listening post enhancements

- DMR/P25 digital voice decoder mode with DSD-FME integration
- WebSDR mode with KiwiSDR audio proxy and websocket-client support
- Listening post waterfall/spectrogram visualization and audio streaming
- Dockerfile updates for mbelib and DSD-FME build dependencies
- New tests for DMR, WebSDR, KiwiSDR, waterfall, and signal guess API
- Chart.js date adapter for time-scale axes

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

pyproject.toml

@@ -33,6 +33,7 @@ dependencies = [
     "flask-limiter>=2.5.4",
     "bleak>=0.21.0",
     "flask-sock",
+    "websocket-client>=1.6.0",
     "requests>=2.28.0",
 ]