style: add loading-spinner and overlay CSS classes

apps/frontend/src/styles.css

@@ -50,3 +50,33 @@ a {
   animation: shimmer 1.5s ease-in-out infinite;
   border-radius: 4px;
 }
+
+@keyframes loading-spin {
+  to { transform: rotate(360deg); }
+}
+
+.loading-spinner {
+  width: 20px;
+  height: 20px;
+  border: 2px solid var(--color-bg);
+  border-top-color: var(--color-primary);
+  border-radius: 50%;
+  animation: loading-spin 0.8s linear infinite;
+}
+
+.table-container {
+  position: relative;
+}
+
+.table-loading-overlay {
+  position: absolute;
+  inset: 0;
+  background: rgba(255, 255, 255, 0.65);
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  flex-direction: column;
+  gap: 12px;
+  transition: opacity 0.2s ease;
+  z-index: 1;
+}