Add smooth animations across WebUI for modern feel

- Tab panels: fade-in with subtle translateY on switch
- Cards: hover lift (translateY -2px), staggered entrance animation
- Modals: spring-curve entrance with backdrop blur
- Buttons: press feedback (scale down on :active)
- Toggle switches: spring overshoot on knob transition
- Toast: smooth bounce-in replaces jarring shake
- Sections: animated height collapse/expand with chevron rotation
- Command palette: slide-down entrance animation
- Theme switch: smooth color transitions on key elements
- Dashboard: section collapse animation, target row hover
- Respects prefers-reduced-motion globally

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

server/src/wled_controller/static/css/base.css

@@ -71,3 +71,23 @@ body.modal-open {
     margin: 0 auto;
     padding: 20px;
 }
+
+/* ── Smooth theme transitions ── */
+body,
+.card,
+.template-card,
+.modal-content,
+.dashboard-target,
+.perf-chart-card,
+header {
+    transition: background-color 0.3s ease, color 0.3s ease, border-color 0.3s ease;
+}
+
+/* ── Respect reduced motion preference ── */
+@media (prefers-reduced-motion: reduce) {
+    *, *::before, *::after {
+        animation-duration: 0.01ms !important;
+        animation-iteration-count: 1 !important;
+        transition-duration: 0.01ms !important;
+    }
+}