refactor(ui): unify and modernize in-app toast notifications

- Created root-level ToastProvider and useToast hook
- Replaced scattered ad-hoc toast states with unified provider
- Updated Settings, Scheduler, Speed Limiter, App, and DownloadTable to use ToastContext
- Added variant support (success, info, warning, error) with distinct styling
- Refined toast animations and styling for modern aesthetics
- Adjusted auto-dismiss behavior to ignore actionable or important errors

src/main.tsx

@@ -3,13 +3,16 @@ import { createRoot } from "react-dom/client";
 import "./index.css";
 import App from "./App";
 import { ErrorBoundary } from "./ErrorBoundary";
+import { ToastProvider } from "./contexts/ToastContext";
 
 const rootElement = document.getElementById("root");
 if (rootElement) {
   createRoot(rootElement).render(
     <StrictMode>
       <ErrorBoundary>
-        <App />
+        <ToastProvider>
+          <App />
+        </ToastProvider>
       </ErrorBoundary>
     </StrictMode>,
   );