[ui] files are added instead of replaced when dragged onto upload dialog

webui/src/components/AddModal.svelte

@@ -22,7 +22,16 @@
   $: visible = files.length + URLs.length > 0;
 
   addEmitter.on("files", (ev) => {
-    files = ev;
+    ev.forEach((file) => {
+      if (
+        !files
+          .map((f) => `${f.name}${f.size}`)
+          .includes(`${file.name}${file.size}`)
+      ) {
+        files.push(file);
+      }
+      files = files;
+    });
   });
 
   async function upload() {