Fix PortalRoot hiding the component's menus and tooltips

compound-web 10.4.0 treats a PortalRoot whose root is null as one whose root
is not available yet, so floating-ui never mounts the portal and every tooltip
label, and with it every icon button's accessible name, is missing. The
component defaulted portalRoot to null and wrapped the call unconditionally.

Wrap the call only when the host supplied a root, keeping null as the
not-yet-available case Compound defines, and say so on the prop. Cover it in
CallPortalRoot.test.tsx. Drop the git allowBuilds entry for compound-web now
that it is a release again.

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

component/api.ts

@@ -130,7 +130,9 @@ export interface ElementCallProps {
    * A host that moves Element Call's DOM into another document, such as a
    * Document Picture-in-Picture window, passes that document's body here so
    * that a menu opens in the window its button is in. Changes take effect at
-   * once.
+   * once. `null` means the root is not available yet, as from a callback ref
+   * that has not fired: menus and tooltips wait for it rather than falling
+   * back to the body.
    */
   portalRoot?: HTMLElement | null;
 }