fix: expand kanban column drop zone to full height

The droppable area in kanban columns was limited to near the top,
making it difficult to drop cards lower in the column.

Fixes #18842

Author: JASSBR

packages/twenty-front/src/modules/object-record/record-board/components/RecordBoardColumns.tsx

@@ -7,6 +7,7 @@ import { themeCssVariables } from 'twenty-ui/theme-constants';
 
 const StyledColumnContainer = styled.div`
   display: flex;
+  flex: 1;
 
   & > *:not(:first-of-type) {
     border-left: 1px solid ${themeCssVariables.border.color.light};