- Create BudgetAlertBanner with threshold detection (>=80% budget utilization)
- Display agent names with percentages, warn color for 80-99%, danger for 100%+
- Dismissible per session with auto-reset on new threshold crossings
- View Costs link navigates to costs section
- Accessible with role=alert, aria-live=assertive, keyboard-dismissible
- Framer Motion fade-in/slide-down animation, respects reduced motion
- Positioned after RecoveryBanner in Dashboard layout