Fix MQTT publish for built-in motion detections

[yangs1202]

Summary

• publish MQTT detection payloads for built-in motion detections
• update Home Assistant motion and detection count topics from the built-in motion backend
• keep behavior aligned with API and ONVIF detection paths

Why

The built-in motion detection path stores thresholded detections in the database, but unlike the API detection path it did not call mqtt_publish_detection() or mqtt_set_motion_state(). As a result, Home Assistant discovery topics were created, snapshots continued to publish, but these state topics did not update for streams using model=motion:

• lightnvr/cameras/<stream>/motion
• lightnvr/cameras/<stream>/detection_count
• lightnvr/detections/<stream>

Testing

• Applied the patch to a clean clone.
• Ran git diff --check.
• Built in a Debian sid container with CI-like options:

  cmake .. \
    -DCMAKE_BUILD_TYPE=Release \
    -DCMAKE_EXPORT_COMPILE_COMMANDS=ON \
    -DENABLE_SOD=OFF \
    -DENABLE_GO2RTC=OFF \
    -DBUILD_TESTS=OFF
  cmake --build . -j2

• Confirmed build/bin/lightnvr was produced.

[github-actions]

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