fix: target named login action

Point the login form at the explicit named action used by the server route.

Remove the stale production preview command from the README deployment notes.

src/lib/components/login-form.svelte

@@ -55,7 +55,7 @@
 </script>
 
 <div class={cn("flex flex-col gap-6", className)} bind:this={ref} {...restProps}>
-	<form method="POST" use:enhance>
+	<form action="?/login" method="POST" use:enhance>
 		<Field.Group>
 			<div class="flex flex-col items-center gap-2 text-center">
 				<div class="flex flex-col items-center gap-2 font-medium">