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/templates/index.html

@@ -20,6 +20,7 @@
         <button class="demo-banner-dismiss" onclick="dismissDemoBanner()" aria-label="Dismiss">&times;</button>
     </div>
     <canvas id="bg-anim-canvas"></canvas>
+    <canvas id="bg-effect-canvas"></canvas>
     <div id="bg-effect-layer"></div>
         <div id="connection-overlay" class="connection-overlay" style="display:none" aria-hidden="true">
             <div class="connection-overlay-content">