Codebase review fixes: stability, performance, quality improvements

Stability: Add outer try/except/finally with _running=False cleanup to all 6
processing loop methods (live, color_strip, effect, audio, composite, mapped).
Add exponential backoff on consecutive capture errors in live_stream. Move
audio stream.stop() outside lock scope.

Performance: Replace per-pixel Python loop with np.array().tobytes() in
ddp_client. Vectorize pixelate filter with cv2.resize down+up. Vectorize
gradient rendering with np.searchsorted.

Frontend: Add lockBody/unlockBody re-entrancy counter. Add {once:true} to
fetchWithAuth abort listener. Null ws.onclose before ws.close() in LED preview.

Backend: Remove auth token prefix from log messages. Add atomic_write_json
helper (tempfile + os.replace) and update all 10 stores. Add name uniqueness
checks to all update methods. Fix DELETE status codes to 204 in audio_sources
and value_sources. Fix get_source() silent bug in color_strip_sources.

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

server/src/wled_controller/core/audio/audio_capture.py

@@ -222,6 +222,7 @@ class AudioCaptureManager:
                 return
 
         key = (engine_type, device_index, is_loopback)
+        stream_to_stop = None
         with self._lock:
             if key not in self._streams:
                 logger.warning(f"Attempted to release unknown audio capture: {key}")
@@ -230,23 +231,28 @@ class AudioCaptureManager:
             stream, ref_count = self._streams[key]
             ref_count -= 1
             if ref_count <= 0:
-                stream.stop()
+                stream_to_stop = stream
                 del self._streams[key]
                 logger.info(f"Removed audio capture {key}")
             else:
                 self._streams[key] = (stream, ref_count)
                 logger.debug(f"Released audio capture {key} (ref_count={ref_count})")
+        # Stop outside the lock — stream.stop() joins a thread (up to 5s)
+        if stream_to_stop is not None:
+            stream_to_stop.stop()
 
     def release_all(self) -> None:
         """Stop and remove all capture streams. Called on shutdown."""
         with self._lock:
-            for key, (stream, _) in list(self._streams.items()):
-                try:
-                    stream.stop()
-                except Exception as e:
-                    logger.error(f"Error stopping audio capture {key}: {e}")
+            streams_to_stop = list(self._streams.items())
             self._streams.clear()
-            logger.info("Released all audio capture streams")
+        # Stop outside the lock — each stop() joins a thread
+        for key, (stream, _) in streams_to_stop:
+            try:
+                stream.stop()
+            except Exception as e:
+                logger.error(f"Error stopping audio capture {key}: {e}")
+        logger.info("Released all audio capture streams")
 
     @staticmethod
     def enumerate_devices() -> List[dict]: