feat: complete stage 1 infrastructure

src/components/ui/sonner.tsx

@@ -0,0 +1,22 @@
+import { Toaster as SonnerToaster } from "sonner";
+
+export function Toaster() {
+  return (
+    <SonnerToaster
+      position="top-right"
+      richColors
+      theme="system"
+      toastOptions={{
+        classNames: {
+          toast: "group rounded-md border bg-background text-foreground shadow-lg",
+          title: "text-sm font-semibold",
+          description: "text-sm text-muted-foreground",
+          closeButton:
+            "absolute right-2 top-2 rounded-full p-1 text-muted-foreground transition-colors hover:bg-muted hover:text-foreground",
+          actionButton:
+            "rounded-md bg-primary px-3 py-1 text-xs font-medium text-primary-foreground transition-colors hover:bg-primary/90",
+        },
+      }}
+    />
+  );
+}