style: improve current provider visual feedback and toast duration

- Add light blue ring border to active provider card instead of solid border
- Fix border flashing issue when switching providers
- Reduce toast notification duration from 4s to 2s for better UX

src/components/ui/sonner.tsx

@@ -7,6 +7,7 @@ export function Toaster() {
       richColors
       theme="system"
       toastOptions={{
+        duration: 2000,
         classNames: {
           toast:
             "group rounded-md border bg-background text-foreground shadow-lg",