Remove redundant boundary checks for section movement in TrainingUnitSectionsEditor

- Eliminated the checks that prevented section movement across slots when crossing the boundary between 'parallel' and 'whole_group' phases, streamlining the section management logic and improving code clarity.

frontend/src/components/TrainingUnitSectionsEditor.jsx

@@ -928,27 +928,6 @@ export default function TrainingUnitSectionsEditor({
       }
     }
 
-    let crossesParallelWholePlanBoundary = false
-    if (
-      enableParallelPhaseControls &&
-      insertBeforeIdx >= 0 &&
-      insertBeforeIdx < list.length
-    ) {
-      const fromK = list[fromSi]?.planLoc?.phaseKind
-      const toK = list[insertBeforeIdx]?.planLoc?.phaseKind
-      crossesParallelWholePlanBoundary =
-        (fromK === 'parallel' && toK === 'whole_group') ||
-        (fromK === 'whole_group' && toK === 'parallel')
-    }
-
-    if (
-      enableParallelPhaseControls &&
-      (insertBeforeIdx === fromSi || insertBeforeIdx === fromSi + 1) &&
-      !crossesParallelWholePlanBoundary
-    ) {
-      return
-    }
-
     if (
       typeof onMoveSectionsAcrossSlots === 'function' &&
       sectionToSlot >= 0 &&