fix(e2e): scope Create button locator to message-input-root

The unscoped getByRole("button", { name: "Create" }) matched sidebar
"Create a new workspace" buttons from other test suites. Scoping to
message-input-root targets only the Composer submit button.

packages/app/e2e/helpers/new-workspace.ts

@@ -169,7 +169,9 @@ export async function clickNewWorkspaceButton(
     timeout: 30_000,
   });
 
-  const createButton = page.getByRole("button", { name: "Create" });
+  const createButton = page
+    .getByTestId("message-input-root")
+    .getByRole("button", { name: "Create" });
   await expect(createButton).toBeVisible({ timeout: 30_000 });
   await createButton.click();
 }