Improve admin panel and sale countdown banner

- Remove 'apply to all' option from sale manager - only selected items
- Fix PLA Translucent to be spool-only (no refill option)
- Sale countdown shows actual max percentage from database
- Update banner design: blue-purple-orange gradient instead of red
- Remove fire emoji and promotional text
- Make percentage number larger and yellow for emphasis
- Change 'do' to 'od' in discount text
- Add shimmer animation for subtle effect

src/styles/index.css

@@ -28,4 +28,18 @@
   .no-transitions * {
     transition: none !important;
   }
+}
+
+/* Shimmer animation for sale banner */
+@keyframes shimmer {
+  0% {
+    transform: translateX(-100%);
+  }
+  100% {
+    transform: translateX(200%);
+  }
+}
+
+.animate-shimmer {
+  animation: shimmer 3s ease-in-out infinite;
 }