Expense Summary

Given a list of expenses, calculate useful totals and identify the largest expense. The final summary should reuse the smaller helper functions.

1. `calculateTotal(expenses)` should return the total amount spent.
2. `calculateCategoryTotal(expenses, category)` should return the total for one category.
3. `findLargestExpense(expenses)` should return the full expense object with the largest amount.
4. `createExpenseSummary(expenses)` should return `total`, `foodTotal`, `transportTotal`, and `largestExpense`.