feat: add svelte-sonner and mode-watcher dependencies, implement Toaster component

src/lib/components/ui/sonner/sonner.svelte

@@ -0,0 +1,20 @@
+<script lang="ts">
+	import { Toaster as Sonner, type ToasterProps as SonnerProps } from "svelte-sonner";
+	import { mode } from "mode-watcher";
+
+	let { ...restProps }: SonnerProps = $props();
+</script>
+
+<Sonner
+	theme={mode.current}
+	class="toaster group"
+	toastOptions={{
+		classes: {
+			toast: "group toast group-[.toaster]:bg-background group-[.toaster]:text-foreground group-[.toaster]:border-border group-[.toaster]:shadow-lg",
+			description: "group-[.toast]:text-muted-foreground",
+			actionButton: "group-[.toast]:bg-primary group-[.toast]:text-primary-foreground",
+			cancelButton: "group-[.toast]:bg-muted group-[.toast]:text-muted-foreground",
+		},
+	}}
+	{...restProps}
+/>