feat: expand appearance with shader effects and new style presets

Add 5 WebGL shader background effects (Aurora, Plasma, Digital Rain,
Starfield, Warp Tunnel) via a new bg-shaders.ts engine that shares
a dedicated canvas. Add 5 style presets (Sakura, Ocean, Copper, Vapor,
Monolith) with distinctive font pairings. Remove CSS particles effect
in favor of shader-based alternatives. Fix dot grid visibility and
tune all shader intensities for subtle ambient appearance.

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

@@ -14,6 +14,7 @@ import { t, initLocale, changeLocale } from './core/i18n.ts';
 // Layer 1.5: visual effects
 import { initCardGlare } from './core/card-glare.ts';
 import { initBgAnim, updateBgAnimAccent, updateBgAnimTheme } from './core/bg-anim.ts';
+import { initBgShaders } from './core/bg-shaders.ts';
 import { initTabIndicator, updateTabIndicator } from './core/tab-indicator.ts';
 
 // Layer 2: ui
@@ -634,6 +635,7 @@ document.addEventListener('DOMContentLoaded', async () => {
     // Initialize visual effects
     initCardGlare();
     initBgAnim();
+    initBgShaders();
     initAppearance();
     initTabIndicator();
     updateBgAnimTheme(document.documentElement.getAttribute('data-theme') !== 'light');