Returns the trainee's nutrition for the given calendar day. The full object is always returned with three parts: menu — the coach's nutrition menu (template) that applies to the weekday, including its id, name, type (DETAILED_PLAN or MACRO_GOALS) and macro goals (calories/protein/carbs/fats); meals — the foods the trainee logged themselves, grouped by meal, with per-serving macros (the coach's templated plan foods are excluded); and totals — the daily totals across logged foods. menu is null when no active template covers the weekday; meals is an empty array when the trainee logged no food that day.