Add missing description for hidden_until_found prop

- Complete prop descriptions for CollapsiblePanel class
- Both hidden_until_found and keep_mounted now have descriptions from Base UI docs
- Ensures consistency between .py and .pyi files

Co-Authored-By: Carlos Cutillas <[email protected]>

Author: devin-ai-integration[bot]

reflex_ui/components/base/collapsible.py

@@ -73,6 +73,7 @@ class CollapsiblePanel(CollapsibleBaseComponent):
 
     tag = "Collapsible.Panel"
 
+    # Allows the browser's built-in page search to find and expand the panel contents. Overrides the `keepMounted` prop and uses `hidden="until-found"` to hide the element without removing it from the DOM.
     hidden_until_found: Var[bool]
 
     # Whether to keep the element in the DOM while the panel is hidden. This prop is ignored when `hiddenUntilFound` is used.