Codebase review: stability, performance, usability, and i18n fixes

Stability:
- Fix race condition: set _is_running before create_task in target processors
- Await probe task after cancel in wled_target_processor
- Replace raw fetch() with fetchWithAuth() across devices, kc-targets, pattern-templates
- Add try/catch to showTestTemplateModal in streams.js
- Wrap blocking I/O in asyncio.to_thread (picture_targets, system restore)
- Fix dashboardStopAll to filter only running targets with ok guard

Performance:
- Vectorize fire effect spark loop with numpy in effect_stream
- Vectorize FFT band binning with cumulative sum in analysis.py
- Rewrite pixel_processor with vectorized numpy (accept ndarray or list)
- Add httpx.AsyncClient connection pooling with lock in wled_provider
- Optimize _send_pixels_http to avoid np.hstack allocation in wled_client
- Mutate chart arrays in-place in dashboard, perf-charts, targets
- Merge dashboard 2-batch fetch into single Promise.all
- Hoist frame_time outside loop in mapped_stream

Usability:
- Fix health check interval load/save in device settings
- Swap confirm modal button classes (No=secondary, Yes=danger)
- Add aria-modal to audio/value source editors, fix close button aria-labels
- Add modal footer close button to settings modal
- Add dedicated calibration LED count validation error keys

i18n:
- Replace ~50 hardcoded English strings with t() calls across 12 JS files
- Add 50 new keys to en.json, ru.json, zh.json
- Localize inline toasts in index.html with window.t fallback
- Add data-i18n to command palette footer
- Add localization policy to CLAUDE.md

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

server/src/wled_controller/core/processing/effect_stream.py

@@ -356,12 +356,17 @@ class EffectColorStripStream(ColorStripStream):
             new_heat[-1] = heat[-1] * 0.5
             heat[:] = new_heat
 
-        # Sparks at the bottom
+        # Sparks at the bottom (vectorized)
         spark_zone = max(1, n // 8)
         spark_prob = 0.3 * intensity
-        for i in range(spark_zone):
-            if np.random.random() < spark_prob:
-                heat[i] = min(1.0, heat[i] + 0.4 + 0.6 * np.random.random())
+        rng = np.random.random(spark_zone)
+        mask = rng < spark_prob
+        if mask.any():
+            heat[:spark_zone] = np.where(
+                mask,
+                np.minimum(1.0, heat[:spark_zone] + 0.4 + 0.6 * np.random.random(spark_zone)),
+                heat[:spark_zone],
+            )
 
         # Map heat to palette (pre-allocated scratch)
         np.multiply(heat, 255, out=self._s_f32_a)

server/src/wled_controller/core/processing/kc_target_processor.py

@@ -174,8 +174,8 @@ class KCTargetProcessor(TargetProcessor):
         self._latest_colors = None
 
         # Start processing task
-        self._task = asyncio.create_task(self._processing_loop())
         self._is_running = True
+        self._task = asyncio.create_task(self._processing_loop())
 
         logger.info(f"Started KC processing for target {self._target_id}")
         self._ctx.fire_event({"type": "state_change", "target_id": self._target_id, "processing": True})

server/src/wled_controller/core/processing/mapped_stream.py

@@ -152,10 +152,10 @@ class MappedColorStripStream(ColorStripStream):
     # ── Processing loop ─────────────────────────────────────────
 
     def _processing_loop(self) -> None:
+        frame_time = 1.0 / self._fps
         try:
             while self._running:
                 loop_start = time.perf_counter()
-                frame_time = 1.0 / self._fps
 
                 try:
                     target_n = self._led_count

server/src/wled_controller/core/processing/wled_target_processor.py

@@ -160,8 +160,8 @@ class WledTargetProcessor(TargetProcessor):
 
         # Reset metrics and start loop
         self._metrics = ProcessingMetrics(start_time=datetime.utcnow())
-        self._task = asyncio.create_task(self._processing_loop())
         self._is_running = True
+        self._task = asyncio.create_task(self._processing_loop())
 
         logger.info(f"Started processing for target {self._target_id}")
         self._ctx.fire_event({"type": "state_change", "target_id": self._target_id, "processing": True})
@@ -889,6 +889,10 @@ class WledTargetProcessor(TargetProcessor):
                 await _probe_client.aclose()
             if _probe_task is not None and not _probe_task.done():
                 _probe_task.cancel()
+                try:
+                    await _probe_task
+                except (asyncio.CancelledError, Exception):
+                    pass
             self._device_reachable = None
             self._metrics.device_streaming_reachable = None
             logger.info(f"Processing loop ended for target {self._target_id}")