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/static/locales/zh.json

@@ -992,5 +992,54 @@
   "settings.saved_backups.download": "下载",
   "settings.saved_backups.delete": "删除",
   "settings.saved_backups.delete_confirm": "删除此备份文件？",
-  "settings.saved_backups.delete_error": "删除备份失败"
+  "settings.saved_backups.delete_error": "删除备份失败",
+  "device.error.power_off_failed": "关闭设备失败",
+  "device.removed": "设备已移除",
+  "device.error.remove_failed": "移除设备失败",
+  "device.error.settings_load_failed": "加载设备设置失败",
+  "device.error.brightness": "更新亮度失败",
+  "device.error.required": "请填写所有字段",
+  "device.error.update": "更新设备失败",
+  "device.error.save": "保存设置失败",
+  "device_discovery.error.fill_all_fields": "请填写所有字段",
+  "device_discovery.added": "设备添加成功",
+  "device_discovery.error.add_failed": "添加设备失败",
+  "calibration.error.load_failed": "加载校准失败",
+  "calibration.error.css_load_failed": "加载色带源失败",
+  "calibration.error.test_toggle_failed": "切换测试边缘失败",
+  "calibration.saved": "校准已保存",
+  "calibration.error.save_failed": "保存校准失败",
+  "calibration.error.led_count_mismatch": "LED总数必须等于设备LED数量",
+  "calibration.error.led_count_exceeded": "校准的LED超过了LED总数",
+  "dashboard.error.profile_toggle_failed": "切换配置文件失败",
+  "dashboard.error.start_failed": "启动处理失败",
+  "dashboard.error.stop_failed": "停止处理失败",
+  "dashboard.error.autostart_toggle_failed": "切换自动启动失败",
+  "dashboard.error.stop_all": "停止所有目标失败",
+  "target.error.editor_open_failed": "打开目标编辑器失败",
+  "target.error.start_failed": "启动目标失败",
+  "target.error.stop_failed": "停止目标失败",
+  "target.error.clone_failed": "克隆目标失败",
+  "target.error.autostart_toggle_failed": "切换自动启动失败",
+  "target.error.delete_failed": "删除目标失败",
+  "audio_source.error.load": "加载音频源失败",
+  "audio_template.error.clone_failed": "克隆音频模板失败",
+  "value_source.error.load": "加载数值源失败",
+  "color_strip.error.editor_open_failed": "打开色带编辑器失败",
+  "color_strip.error.clone_failed": "克隆色带源失败",
+  "color_strip.error.delete_failed": "删除色带源失败",
+  "pattern.error.editor_open_failed": "打开图案模板编辑器失败",
+  "pattern.error.clone_failed": "克隆图案模板失败",
+  "pattern.error.delete_failed": "删除图案模板失败",
+  "pattern.error.capture_bg_failed": "捕获背景失败",
+  "stream.error.clone_picture_failed": "克隆图片源失败",
+  "stream.error.clone_capture_failed": "克隆捕获模板失败",
+  "stream.error.clone_pp_failed": "克隆后处理模板失败",
+  "kc_target.error.editor_open_failed": "打开关键颜色编辑器失败",
+  "kc_target.error.clone_failed": "克隆关键颜色目标失败",
+  "kc_target.error.delete_failed": "删除关键颜色目标失败",
+  "theme.switched.dark": "已切换到深色主题",
+  "theme.switched.light": "已切换到浅色主题",
+  "accent.color.updated": "强调色已更新",
+  "search.footer": "↑↓ 导航 · Enter 选择 · Esc 关闭"
 }