Add semi-transparent blurred tab icon as background watermark

Large SVG icon on the right side of the viewport reflects the active tab,
crossfades on tab switch. Also removes overflow:hidden from cards to fix
color picker clipping.

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

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

@@ -13,6 +13,7 @@ import { t, initLocale, changeLocale } from './core/i18n.js';
 // Layer 1.5: visual effects
 import { initCardGlare } from './core/card-glare.js';
 import { initBgAnim, updateBgAnimAccent, updateBgAnimTheme } from './core/bg-anim.js';
+import { initTabIndicator, updateTabIndicator } from './core/tab-indicator.js';
 
 // Layer 2: ui
 import {
@@ -173,6 +174,7 @@ Object.assign(window, {
     // visual effects (called from inline <script>)
     _updateBgAnimAccent: updateBgAnimAccent,
     _updateBgAnimTheme: updateBgAnimTheme,
+    _updateTabIndicator: updateTabIndicator,
 
     // core / ui
     toggleHint,
@@ -539,6 +541,7 @@ document.addEventListener('DOMContentLoaded', async () => {
     // Initialize visual effects
     initCardGlare();
     initBgAnim();
+    initTabIndicator();
     updateBgAnimTheme(document.documentElement.getAttribute('data-theme') !== 'light');
     const accent = localStorage.getItem('accentColor') || '#4CAF50';
     updateBgAnimAccent(accent);