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/templates/modals/css-editor.html

@@ -363,6 +363,19 @@
                                oninput="document.getElementById('css-editor-api-input-timeout-val').textContent = parseFloat(this.value).toFixed(1)">
                     </div>
 
+                    <div class="form-group">
+                        <div class="label-row">
+                            <label for="css-editor-api-input-interpolation" data-i18n="color_strip.api_input.interpolation">LED Interpolation:</label>
+                            <button type="button" class="hint-toggle" onclick="toggleHint(this)" title="?" data-i18n-aria-label="aria.hint">?</button>
+                        </div>
+                        <small class="input-hint" style="display:none" data-i18n="color_strip.api_input.interpolation.hint">How to resize incoming LED data when its count differs from the device's LED count.</small>
+                        <select id="css-editor-api-input-interpolation">
+                            <option value="linear">Linear</option>
+                            <option value="nearest">Nearest</option>
+                            <option value="none">None</option>
+                        </select>
+                    </div>
+
                     <div class="form-group" id="css-editor-api-input-endpoints-group">
                         <div class="label-row">
                             <label data-i18n="color_strip.api_input.endpoints">Push Endpoints:</label>