fix(e2e): clear the document file input after sending

Native file inputs only fire onChange when their value changes, so
re-selecting the same PDF in the harness did nothing. Clears the input's
value after the send callback runs. Document input only, per review scope.

Author: dangreenberggit

testing/e2e/src/components/ChatUI.tsx

@@ -278,6 +278,9 @@ export function ChatUI({
               if (file && text && onSendMessageWithDocument) {
                 onSendMessageWithDocument(text, file)
                 setInput('')
+                // Clear the file input so re-selecting the same PDF fires
+                // onChange again.
+                e.target.value = ''
               }
             }}
           />