Filter audio devices by engine type and update tutorial steps

- Add enumerate_devices_by_engine() returning per-engine device lists
  without cross-engine dedup so frontend can filter correctly
- API /audio-devices now includes by_engine dict alongside flat list
- Frontend caches per-engine data, filters device dropdown by selected
  template's engine_type, refreshes on template change
- Reorder getting-started tutorial: add API docs and accent color steps
- Fix tutorial trigger button focus outline persisting on step 2
- Use accent color variable for tutorial pulse ring animation

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

server/src/wled_controller/static/locales/zh.json

@@ -222,8 +222,10 @@
   "tour.sources": "来源 — 管理捕获模板、图片来源、音频来源和色带。",
   "tour.profiles": "配置文件 — 将目标分组，并通过时间、音频或数值条件自动切换。",
   "tour.settings": "设置 — 备份和恢复配置，管理自动备份。",
+  "tour.api": "API 文档 — 基于 Swagger 的交互式 REST API 文档。",
   "tour.search": "搜索 — 使用 Ctrl+K 快速查找并导航到任意实体。",
   "tour.theme": "主题 — 在深色和浅色模式之间切换。",
+  "tour.accent": "主题色 — 自定义界面的强调颜色。",
   "tour.language": "语言 — 选择您偏好的界面语言。",
   "tour.restart": "重新开始导览",
   "tour.dash.perf": "性能 — 实时 FPS 图表、延迟指标和轮询间隔控制。",