Fix: Catchment dropdown should not float (#1272)

[Leo-Stephen]

Fix: Catchment dropdown should not float (#1272)

This PR fixes issue #1272 where the Catchment dropdown floats when scrolling instead of staying with its input field.

Solution

After investigating several approaches, I found that replacing AutocompleteInput with SelectInput provides the most reliable solution:

• It uses native HTML select elements which browsers handle correctly during scrolling
• It maintains compatibility with all existing props and parent components
• The trade-off is losing typeahead functionality, but gaining proper scroll behavior

The root cause was related to how Material-UI v4 and react-admin 2.7.2 handle dropdown positioning in different contexts.