Add CPU/GPU names on perf charts, reusable color picker, and header toolbar redesign

- Show CPU and GPU model names as overlays on performance chart cards
- Add cpu_name field to performance API with cross-platform detection
- Extract reusable color-picker popover module (9 presets + custom picker)
- Per-chart color customization for CPU/RAM/GPU performance charts
- Redesign header: compact toolbar container with icon-only buttons
- Compact language dropdown (EN/RU/ZH), icon-only login/logout
- Use accent color for FPS charts, range slider accent, dashboard icons

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

server/src/wled_controller/static/css/dashboard.css

@@ -104,6 +104,7 @@
 .dashboard-target-icon {
     font-size: 1rem;
     flex-shrink: 0;
+    color: var(--primary-text-color);
 }
 
 .dashboard-target-name {
@@ -317,7 +318,7 @@
     display: flex;
     justify-content: space-between;
     align-items: center;
-    margin-bottom: 4px;
+    margin-bottom: 0;
 }
 
 .perf-chart-label {
@@ -328,14 +329,33 @@
     color: var(--text-secondary);
 }
 
+.perf-chart-subtitle {
+    position: absolute;
+    top: 0;
+    left: 0;
+    font-size: 0.6rem;
+    font-weight: 400;
+    color: var(--text-muted);
+    overflow: hidden;
+    text-overflow: ellipsis;
+    white-space: nowrap;
+    max-width: calc(100% - 4px);
+    pointer-events: none;
+    opacity: 0.7;
+    z-index: 1;
+}
+
 .perf-chart-value {
     font-size: 0.85rem;
     font-weight: 700;
+    color: var(--primary-text-color);
 }
 
-.perf-chart-value.cpu { color: #2196F3; }
-.perf-chart-value.ram { color: #4CAF50; }
-.perf-chart-value.gpu { color: #FF9800; }
+.perf-chart-label .color-picker-swatch {
+    width: 12px;
+    height: 12px;
+    vertical-align: middle;
+}
 
 .perf-chart-unavailable {
     text-align: center;