feat: implement resumable chunked media upload with progress indicators in admin UI

frontend/src/style.css

@@ -645,6 +645,22 @@ select {
   gap: var(--space-2);
 }
 
+.upload-dropzone.is-dragover {
+  border-color: var(--brand);
+  background: #e6f6ef;
+}
+
+.upload-progress {
+  display: grid;
+  gap: var(--space-1);
+  width: min(540px, 100%);
+}
+
+.upload-progress progress {
+  width: 100%;
+  height: 0.75rem;
+}
+
 .stat-grid {
   display: grid;
   grid-template-columns: repeat(4, minmax(0, 1fr));