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/en.json

@@ -1061,6 +1061,14 @@
     "color_strip.api_input.endpoints": "Push Endpoints:",
     "color_strip.api_input.endpoints.hint": "Use these URLs to push LED color data from your external application. REST accepts JSON, WebSocket accepts both JSON and raw binary frames.",
     "color_strip.api_input.save_first": "Save the source first to see the push endpoint URLs.",
+    "color_strip.api_input.interpolation": "LED Interpolation:",
+    "color_strip.api_input.interpolation.hint": "How to resize incoming LED data when its count differs from the device's LED count. Linear gives smooth blending, Nearest preserves sharp edges, None truncates or zero-pads.",
+    "color_strip.api_input.interpolation.linear": "Linear",
+    "color_strip.api_input.interpolation.linear.desc": "Smooth blending between LEDs",
+    "color_strip.api_input.interpolation.nearest": "Nearest",
+    "color_strip.api_input.interpolation.nearest.desc": "Sharp edges, no blending",
+    "color_strip.api_input.interpolation.none": "None",
+    "color_strip.api_input.interpolation.none.desc": "Truncate or zero-pad",
     "color_strip.type.notification": "Notification",
     "color_strip.type.notification.desc": "One-shot effect on webhook trigger",
     "color_strip.type.notification.hint": "Fires a one-shot visual effect (flash, pulse, sweep) when triggered via a webhook. Designed for use as a composite layer over a persistent base source.",