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/devices/wled_client.py

@@ -404,8 +404,13 @@ class WLEDClient(LEDClient):
         """
         try:
             # Build indexed pixel array: [led_index, r, g, b, ...]
-            indices = np.arange(len(pixels), dtype=np.int32).reshape(-1, 1)
-            indexed_pixels = np.hstack([indices, pixels.astype(np.int32)]).ravel().tolist()
+            n = len(pixels)
+            flat = np.empty(n * 4, dtype=np.int32)
+            flat[0::4] = np.arange(n, dtype=np.int32)
+            flat[1::4] = pixels[:, 0]
+            flat[2::4] = pixels[:, 1]
+            flat[3::4] = pixels[:, 2]
+            indexed_pixels = flat.tolist()
 
             # Build WLED JSON state
             payload = {

server/src/wled_controller/core/devices/wled_provider.py

@@ -24,6 +24,25 @@ DEFAULT_SCAN_TIMEOUT = 3.0
 class WLEDDeviceProvider(LEDDeviceProvider):
     """Provider for WLED LED controllers."""
 
+    def __init__(self):
+        self._http_client: Optional[httpx.AsyncClient] = None
+        self._client_lock = asyncio.Lock()
+
+    async def _get_client(self) -> httpx.AsyncClient:
+        """Return a shared HTTP client (connection-pooled, thread-safe init)."""
+        if self._http_client is not None and not self._http_client.is_closed:
+            return self._http_client
+        async with self._client_lock:
+            if self._http_client is None or self._http_client.is_closed:
+                self._http_client = httpx.AsyncClient(timeout=5.0)
+        return self._http_client
+
+    async def close(self):
+        """Close the shared HTTP client."""
+        if self._http_client is not None and not self._http_client.is_closed:
+            await self._http_client.aclose()
+            self._http_client = None
+
     @property
     def device_type(self) -> str:
         return "wled"
@@ -158,46 +177,46 @@ class WLEDDeviceProvider(LEDDeviceProvider):
 
     async def get_brightness(self, url: str) -> int:
         url = url.rstrip("/")
-        async with httpx.AsyncClient(timeout=5.0) as http_client:
-            resp = await http_client.get(f"{url}/json/state")
-            resp.raise_for_status()
-            state = resp.json()
-            return state.get("bri", 255)
+        client = await self._get_client()
+        resp = await client.get(f"{url}/json/state")
+        resp.raise_for_status()
+        state = resp.json()
+        return state.get("bri", 255)
 
     async def set_brightness(self, url: str, brightness: int) -> None:
         url = url.rstrip("/")
-        async with httpx.AsyncClient(timeout=5.0) as http_client:
-            resp = await http_client.post(
-                f"{url}/json/state",
-                json={"bri": brightness},
-            )
-            resp.raise_for_status()
+        client = await self._get_client()
+        resp = await client.post(
+            f"{url}/json/state",
+            json={"bri": brightness},
+        )
+        resp.raise_for_status()
 
     async def get_power(self, url: str, **kwargs) -> bool:
         url = url.rstrip("/")
-        async with httpx.AsyncClient(timeout=5.0) as http_client:
-            resp = await http_client.get(f"{url}/json/state")
-            resp.raise_for_status()
-            return resp.json().get("on", False)
+        client = await self._get_client()
+        resp = await client.get(f"{url}/json/state")
+        resp.raise_for_status()
+        return resp.json().get("on", False)
 
     async def set_power(self, url: str, on: bool, **kwargs) -> None:
         url = url.rstrip("/")
-        async with httpx.AsyncClient(timeout=5.0) as http_client:
-            resp = await http_client.post(
-                f"{url}/json/state",
-                json={"on": on},
-            )
-            resp.raise_for_status()
+        client = await self._get_client()
+        resp = await client.post(
+            f"{url}/json/state",
+            json={"on": on},
+        )
+        resp.raise_for_status()
 
     async def set_color(self, url: str, color: Tuple[int, int, int], **kwargs) -> None:
         """Set WLED to a solid color using the native segment color API."""
         url = url.rstrip("/")
-        async with httpx.AsyncClient(timeout=5.0) as http_client:
-            resp = await http_client.post(
-                f"{url}/json/state",
-                json={
-                    "on": True,
-                    "seg": [{"col": [[color[0], color[1], color[2]]], "fx": 0}],
-                },
-            )
-            resp.raise_for_status()
+        client = await self._get_client()
+        resp = await client.post(
+            f"{url}/json/state",
+            json={
+                "on": True,
+                "seg": [{"col": [[color[0], color[1], color[2]]], "fx": 0}],
+            },
+        )
+        resp.raise_for_status()