feat(worksheets): Phase 7 - Add operator to auto-save persistence

Updates useWorksheetAutoSave hook to persist operator field:
- Add operator to destructured fields
- Include operator in saved config object

This ensures the user's operator selection (addition/subtraction/mixed)
is preserved across sessions.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

apps/web/src/app/create/worksheets/addition/hooks/useWorksheetAutoSave.ts

@@ -52,6 +52,7 @@ export function useWorksheetAutoSave(
           orientation,
           name,
           digitRange,
+          operator,
           pAnyStart,
           pAllStart,
           interpolate,
@@ -81,6 +82,7 @@ export function useWorksheetAutoSave(
               orientation,
               name,
               digitRange,
+              operator,
               pAnyStart,
               pAllStart,
               interpolate,