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/features/tabs.js

@@ -37,6 +37,9 @@ export function switchTab(name, { updateHash = true, skipLoad = false } = {}) {
     document.querySelectorAll('.tab-panel').forEach(panel => panel.classList.toggle('active', panel.id === `tab-${name}`));
     localStorage.setItem('activeTab', name);
 
+    // Update background tab indicator
+    if (typeof window._updateTabIndicator === 'function') window._updateTabIndicator(name);
+
     // Restore scroll position for this tab
     requestAnimationFrame(() => window.scrollTo(0, _tabScrollPositions[name] || 0));