Wrap initiative rolls with undo so they produce undo entries

Initiative rolls (single and bulk) called makeStore() directly from
useInitiativeRolls, bypassing the withUndo wrapper. Expose withUndo
from the encounter context and wrap both roll paths.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/web/src/hooks/use-encounter.ts

@@ -430,5 +430,6 @@ export function useEncounter() {
 		undo: undoAction,
 		redo: redoAction,
 		makeStore,
+		withUndo,
 	} as const;
 }