fix(file-manager): accept OS file drops over existing rows (#1484)

* fix(file-manager): accept OS file drops over existing rows

* test(file-manager): target the file label in drop tests

* test(css): exercise the configured PostCSS plugin chain

* test(identity): preserve full Ed25519 public keys in fixtures

* test(remote-desktop): always mutate ciphertext in tamper test

plugins/file-manager/src/frontend/FileManagerGrid.tsx

@@ -458,6 +458,9 @@ export function FileManagerGrid({
   };
 
   const handleFileDrop = (e: React.DragEvent, targetFile: FileItem) => {
+    // OS drops belong to the pane's upload handler, even over an existing row.
+    if (dragState.type !== "internal" && !isLocalFilesDrag(e.dataTransfer))
+      return;
     e.preventDefault();
     e.stopPropagation();