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/static/js/core/api.js

@@ -36,7 +36,7 @@ export async function fetchWithAuth(url, options = {}) {
     for (let attempt = 0; attempt < maxAttempts; attempt++) {
         const controller = new AbortController();
         if (fetchOpts.signal) {
-            fetchOpts.signal.addEventListener('abort', () => controller.abort());
+            fetchOpts.signal.addEventListener('abort', () => controller.abort(), { once: true });
         }
         const timer = setTimeout(() => controller.abort(), timeout);
         try {

server/src/wled_controller/static/js/core/ui.js

@@ -56,17 +56,26 @@ export function setupBackdropClose(modal, closeFn) {
     modal._backdropCloseSetup = true;
 }
 
+let _lockCount = 0;
+let _savedScrollY = 0;
+
 export function lockBody() {
-    const scrollY = window.scrollY;
-    document.body.style.top = `-${scrollY}px`;
-    document.body.classList.add('modal-open');
+    if (_lockCount === 0) {
+        _savedScrollY = window.scrollY;
+        document.body.style.top = `-${_savedScrollY}px`;
+        document.body.classList.add('modal-open');
+    }
+    _lockCount++;
 }
 
 export function unlockBody() {
-    const scrollY = parseInt(document.body.style.top || '0', 10) * -1;
-    document.body.classList.remove('modal-open');
-    document.body.style.top = '';
-    window.scrollTo(0, scrollY);
+    if (_lockCount <= 0) return;
+    _lockCount--;
+    if (_lockCount === 0) {
+        document.body.classList.remove('modal-open');
+        document.body.style.top = '';
+        window.scrollTo(0, _savedScrollY);
+    }
 }
 
 export function openLightbox(imageSrc, statsHtml) {

server/src/wled_controller/static/js/features/targets.js

@@ -1102,6 +1102,7 @@ function connectLedPreviewWS(targetId) {
 function disconnectLedPreviewWS(targetId) {
     const ws = ledPreviewWebSockets[targetId];
     if (ws) {
+        ws.onclose = null;
         ws.close();
         delete ledPreviewWebSockets[targetId];
     }