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

TODO-css-improvements.md

@@ -81,9 +81,9 @@ Need to research HAOS communication options first (WebSocket API, REST API, MQTT
 
 ### `api_input`
 
-- [ ] Crossfade transition when new data arrives
-- [ ] Interpolation when incoming LED count differs from strip count
-- [ ] Last-write-wins from any client (no multi-source blending)
+- [x] ~~Crossfade transition~~ — won't do: external client owns temporal transitions; crossfading on our side would double-smooth
+- [x] Interpolation when incoming LED count differs from strip count (linear/nearest/none modes)
+- [x] Last-write-wins from any client — already the default behavior (push overwrites buffer)
 
 ## Architectural / Pipeline