feat: add api_input LED interpolation; fix LED preview, FPS charts, dashboard layout

API Input:
- Add interpolation mode (linear/nearest/none) for LED count mismatch
  between incoming data and device LED count
- New IconSelect in editor, i18n for en/ru/zh
- Mark crossfade as won't-do (client owns temporal transitions)
- Mark last-write-wins as already implemented

LED Preview:
- Fix zone-mode preview parsing composite wire format (0xFE header
  bytes were rendered as color data, garbling multi-zone previews)
- Fix _restoreLedPreviewState to handle zone-mode panels

FPS Charts:
- Seed target card charts from server metrics-history on first load
- Add fetchMetricsHistory() with 5s TTL cache shared across
  dashboard, targets, perf-charts, and graph-editor
- Fix chart padding: pass maxSamples per caller (120 for dashboard,
  30 for target cards) instead of hardcoded 120
- Fix dashboard chart empty on tab switch (always fetch server history)
- Left-pad with nulls for consistent chart width across targets

Dashboard:
- Fix metrics row alignment (grid layout with fixed column widths)
- Fix FPS label overflow into uptime column

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

@@ -1044,6 +1044,14 @@
     "color_strip.api_input.endpoints": "推送端点：",
     "color_strip.api_input.endpoints.hint": "使用这些 URL 从外部应用程序推送 LED 颜色数据。REST 接受 JSON，WebSocket 接受 JSON 和原始二进制帧。",
     "color_strip.api_input.save_first": "请先保存源以查看推送端点 URL。",
+    "color_strip.api_input.interpolation": "LED 插值：",
+    "color_strip.api_input.interpolation.hint": "当传入的 LED 数量与设备 LED 数量不同时如何调整大小。线性提供平滑混合，最近邻保持锐利边缘，无则截断或补零。",
+    "color_strip.api_input.interpolation.linear": "线性",
+    "color_strip.api_input.interpolation.linear.desc": "LED 之间平滑混合",
+    "color_strip.api_input.interpolation.nearest": "最近邻",
+    "color_strip.api_input.interpolation.nearest.desc": "锐利边缘，无混合",
+    "color_strip.api_input.interpolation.none": "无",
+    "color_strip.api_input.interpolation.none.desc": "截断或补零",
     "color_strip.type.notification": "通知",
     "color_strip.type.notification.desc": "通过Webhook触发的一次性效果",
     "color_strip.type.notification.hint": "通过 Webhook 触发时显示一次性视觉效果（闪烁、脉冲、扫描）。设计为组合源中的叠加层。",