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/js/features/perf-charts.ts

@@ -7,7 +7,7 @@ import { Chart, registerables } from 'chart.js';
 Chart.register(...registerables);
 window.Chart = Chart;  // expose globally for targets.js, dashboard.js
 
-import { API_BASE, getHeaders } from '../core/api.ts';
+import { API_BASE, getHeaders, fetchMetricsHistory } from '../core/api.ts';
 import { t } from '../core/i18n.ts';
 import { dashboardPollInterval } from '../core/state.ts';
 import { createColorPicker, registerColorPicker } from '../core/color-picker.ts';
@@ -112,9 +112,8 @@ function _createChart(canvasId: string, key: string): any {
 /** Seed charts from server-side metrics history. */
 async function _seedFromServer(): Promise<void> {
     try {
-        const resp = await fetch(`${API_BASE}/system/metrics-history`, { headers: getHeaders() });
-        if (!resp.ok) return;
-        const data = await resp.json();
+        const data = await fetchMetricsHistory();
+        if (!data) return;
         const samples = data.system || [];
         _history.cpu = samples.map(s => s.cpu).filter(v => v != null);
         _history.ram = samples.map(s => s.ram_pct).filter(v => v != null);