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/features/tabs.js

@@ -2,7 +2,7 @@
  * Tab switching — switchTab, initTabs, startAutoRefresh.
  */
 
-import { apiKey, refreshInterval, setRefreshInterval } from '../core/state.js';
+import { apiKey, refreshInterval, setRefreshInterval, dashboardPollInterval } from '../core/state.js';
 
 export function switchTab(name) {
     document.querySelectorAll('.tab-btn').forEach(btn => btn.classList.toggle('active', btn.dataset.tab === name));
@@ -15,6 +15,7 @@ export function switchTab(name) {
     } else {
         if (typeof window.stopDashboardWS === 'function') window.stopDashboardWS();
         if (typeof window.stopPerfPolling === 'function') window.stopPerfPolling();
+        if (typeof window.stopUptimeTimer === 'function') window.stopUptimeTimer();
         if (name === 'streams') {
             if (typeof window.loadPictureSources === 'function') window.loadPictureSources();
         } else if (name === 'targets') {
@@ -50,5 +51,5 @@ export function startAutoRefresh() {
                 if (typeof window.loadDashboard === 'function') window.loadDashboard();
             }
         }
-    }, 2000));
+    }, dashboardPollInterval));
 }