fix(portal): fall back to document.body when no PortalProvider exists

Update usePortalRoot hook to return document.body as fallback when no
explicit PortalProvider is present, instead of returning null. This
ensures portals render correctly in applications that don't wrap
content in a PortalProvider.

Returns null only in SSR environments where document is undefined.

Author: praisethemoon

packages/baukasten/src/context/PortalProvider.tsx

@@ -134,17 +134,21 @@ export function PortalProvider({ root, children }: PortalProviderProps) {
 
 /**
  * Hook to access the portal root element from context
- * 
- * Returns null if no PortalProvider is present, which signals components
- * to use their default portal behavior.
- * 
- * @returns The portal root element or null
- * 
+ *
+ * Returns the portal root from PortalProvider if present, otherwise falls back
+ * to `document.body`. This ensures portals always render correctly, even without
+ * an explicit PortalProvider wrapper.
+ *
+ * For multi-window applications (like Theia), wrap your content in PortalProvider
+ * with the appropriate root element for that window.
+ *
+ * @returns The portal root element (from context or document.body), or null in SSR
+ *
  * @example
  * ```tsx
  * function MyPortalComponent() {
  *   const portalRoot = usePortalRoot();
- *   
+ *
  *   return (
  *     <FloatingPortal root={portalRoot}>
  *       <div>Portal content</div>
@@ -155,5 +159,7 @@ export function PortalProvider({ root, children }: PortalProviderProps) {
  */
 export function usePortalRoot(): HTMLElement | null {
     const context = useContext(PortalContext);
-    return context.root;
+    // Return the context root if provided, otherwise fall back to document.body
+    // This ensures portals work even without an explicit PortalProvider
+    return context.root ?? (typeof document !== 'undefined' ? document.body : null);
 }