feat: add visual customization presets to Settings > Appearance tab

Add style presets (font + color combinations) and background effect
presets as a new Appearance tab in the settings modal. Style presets
include Default, Midnight, Ember, Arctic, Terminal, and Neon — each
with curated dark/light theme colors and Google Font pairings.
Background effects (Dot Grid, Gradient Mesh, Scanlines, Particles)
use a dedicated overlay div alongside the existing WebGL Noise Field.
All choices persist to localStorage and restore on page load.

server/src/wled_controller/static/js/features/settings.ts

@@ -72,6 +72,10 @@ export function switchSettingsTab(tabId: string): void {
     document.querySelectorAll('.settings-panel').forEach(panel => {
         panel.classList.toggle('active', panel.id === `settings-panel-${tabId}`);
     });
+    // Lazy-render the appearance tab content
+    if (tabId === 'appearance' && typeof window.renderAppearanceTab === 'function') {
+        window.renderAppearanceTab();
+    }
 }
 
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