Add FPS sparkline charts, configurable poll interval, and uptime interpolation

Replace text FPS labels with Chart.js sparklines on running targets,
use emoji icons for metrics, add in-place DOM updates to preserve
chart animations, and add a 1-10s poll interval slider that controls
all dashboard timers. Uptime now ticks every second via client-side
interpolation regardless of poll interval.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/wled_controller/static/js/app.js

@@ -35,9 +35,9 @@ import {
     updateSettingsBaudFpsHint,
 } from './features/devices.js';
 import {
-    loadDashboard, startDashboardWS, stopDashboardWS,
+    loadDashboard, startDashboardWS, stopDashboardWS, stopUptimeTimer,
     dashboardToggleProfile, dashboardStartTarget, dashboardStopTarget, dashboardStopAll,
-    toggleDashboardSection,
+    toggleDashboardSection, changeDashboardPollInterval,
 } from './features/dashboard.js';
 import {
     startPerfPolling, stopPerfPolling,
@@ -157,6 +157,8 @@ Object.assign(window, {
     dashboardStopTarget,
     dashboardStopAll,
     toggleDashboardSection,
+    changeDashboardPollInterval,
+    stopUptimeTimer,
     startPerfPolling,
     stopPerfPolling,