Keep the component's tooltips inside its root

Compound's Tooltip floats its bubble through floating-ui's FloatingPortal,
into the body: outside the element the component build confines its
stylesheet to, so a label tooltip shows as bare text at all times. An
enclosing FloatingPortal rooted at the container makes the nested portals
land inside it instead.

The call goes in an isolating wrapper there, standing in for the standalone
page's #root, so that its footer layer no longer paints above the modals.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

component/PortalRoot.test.tsx

@@ -0,0 +1,43 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { render, screen } from "@testing-library/react";
+import { Tooltip, TooltipProvider } from "@vector-im/compound-web";
+import { afterEach, describe, expect, test } from "vitest";
+
+import { PortalRoot } from "./PortalRoot";
+
+describe("PortalRoot", () => {
+  const root = document.createElement("div");
+  document.body.appendChild(root);
+  afterEach(() => root.replaceChildren());
+
+  // A label tooltip is in the DOM from the start, hidden by the stylesheet until
+  // hovered, which is what makes it show as bare text when it lands outside the
+  // root
+  const tree = (
+    <TooltipProvider>
+      <Tooltip label="Mute microphone">
+        <button>mic</button>
+      </Tooltip>
+    </TooltipProvider>
+  );
+
+  test("Compound's tooltips float into the root", () => {
+    render(<PortalRoot root={root}>{tree}</PortalRoot>);
+    expect(root).toContainElement(
+      screen.getByRole("button", { name: "Mute microphone" }),
+    );
+    expect(root).toContainElement(screen.getByText("Mute microphone"));
+  });
+
+  test("without it they float into the body", () => {
+    render(tree);
+    expect(root).not.toContainElement(screen.getByText("Mute microphone"));
+    expect(document.body).toContainElement(screen.getByText("Mute microphone"));
+  });
+});