Add category budget auto-calculation

The category budgets are now automatically summed to calculate daily, weekly, and monthly budgets.

src/components/BudgetTabContent.tsx

@@ -118,6 +118,7 @@ const BudgetTabContent: React.FC<BudgetTabContentProps> = ({
           <div className="neuro-card p-4">
             <div>
               <h3 className="text-base font-medium mb-3">카테고리별 예산 설정</h3>
+              <p className="text-sm text-gray-500 mb-4">카테고리 예산을 설정하면 일일, 주간, 월간 예산이 자동으로 합산됩니다.</p>
               <CategoryBudgetInputs categoryBudgets={categoryBudgets} handleCategoryInputChange={handleCategoryInputChange} />
               
               <div className="mt-4 border-t pt-3">