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/api/routes/audio_sources.py

@@ -125,7 +125,7 @@ async def update_audio_source(
         raise HTTPException(status_code=400, detail=str(e))
 
 
-@router.delete("/api/v1/audio-sources/{source_id}", tags=["Audio Sources"])
+@router.delete("/api/v1/audio-sources/{source_id}", status_code=204, tags=["Audio Sources"])
 async def delete_audio_source(
     source_id: str,
     _auth: AuthRequired,
@@ -143,7 +143,6 @@ async def delete_audio_source(
                 )
 
         store.delete_source(source_id)
-        return {"status": "deleted", "id": source_id}
     except ValueError as e:
         raise HTTPException(status_code=400, detail=str(e))