[backport cloud/1.42] App Mode dragAndDrop, text output, and scroll shadows (#10963)

Backport of #10122 to cloud/1.42.

Prerequisite for backporting #10364 (Show filename on previews).

## Conflict resolution

- `src/stores/queueStore.test.ts`: accepted PR version — text content is
now previewable (length 1, content assertion) instead of not previewable
(length 0, undefined).

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-10963-backport-cloud-1-42-App-Mode-dragAndDrop-text-output-and-scroll-shadows-33c6d73d3650816ca420cbc0eae96e3b)
by [Unito](https://www.unito.io)

packages/design-system/src/css/style.css

@@ -1901,3 +1901,37 @@ audio.comfy-audio.empty-audio-widget {
     background-position: 0 0;
   }
 }
+
+@utility scroll-shadows-* {
+  overflow: auto;
+
+  background:
+    /* Shadow Cover TOP */
+    linear-gradient(--value(--color-*) 30%, transparent) center top,
+    /* Shadow Cover BOTTOM */
+      linear-gradient(transparent, --value(--color-*) 70%) center bottom,
+    /* Shadow TOP */
+      radial-gradient(
+        farthest-side at 50% 0,
+        color-mix(in oklab, --value(--color-*), #777777 35%),
+        60%,
+        transparent
+      )
+      center top,
+    /* Shadow BOTTOM */
+      radial-gradient(
+        farthest-side at 50% 100%,
+        color-mix(in oklab, --value(--color-*), #777777 35%),
+        60%,
+        transparent
+      )
+      center bottom;
+
+  background-repeat: no-repeat;
+  background-size:
+    300% 40px,
+    300% 40px,
+    300% 14px,
+    300% 14px;
+  background-attachment: local, local, scroll, scroll;
+}