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/style.css

@@ -3284,12 +3284,32 @@ input:-webkit-autofill:focus {
     flex: 0 0 auto;
 }
 
+.dashboard-poll-wrap {
+    margin-left: auto;
+    display: flex;
+    align-items: center;
+    gap: 3px;
+}
+
+.dashboard-poll-slider {
+    width: 48px;
+    height: 12px;
+    accent-color: var(--primary-color);
+    cursor: pointer;
+}
+
+.dashboard-poll-value {
+    font-size: 0.6rem;
+    color: var(--text-secondary);
+    min-width: 18px;
+}
+
 .dashboard-target {
     display: grid;
     grid-template-columns: 1fr auto auto;
     align-items: center;
     gap: 12px;
-    padding: 8px 12px;
+    padding: 6px 12px;
     background: var(--card-bg);
     border: 1px solid var(--border-color);
     border-radius: 6px;
@@ -3358,6 +3378,33 @@ input:-webkit-autofill:focus {
     letter-spacing: 0.3px;
 }
 
+.dashboard-fps-metric {
+    display: flex;
+    align-items: center;
+    gap: 6px;
+    min-width: auto;
+}
+
+.dashboard-fps-sparkline {
+    position: relative;
+    width: 100px;
+    height: 36px;
+}
+
+.dashboard-fps-label {
+    display: flex;
+    flex-direction: column;
+    align-items: center;
+    min-width: 36px;
+    line-height: 1.1;
+}
+
+.dashboard-fps-target {
+    font-weight: 400;
+    opacity: 0.5;
+    font-size: 0.75rem;
+}
+
 .dashboard-target-actions {
     display: flex;
     align-items: center;