Improve Error Toasts Across UI

## ⚠️ #6 Feature: Improve Error Toasts Across UI

### 🧠 Context
Errors are inconsistent and unclear.

### 🎯 Goal
Standardize error handling.

### 🛠️ Tasks
- [ ] Normalize error messages
- [ ] Add retry option
- [ ] Improve styling

### ✅ Acceptance Criteria
- Consistent error UX across app
- Users can retry failed actions

### 🏷️ Labels
frontend, ui