feat: add create and message page UI

Co-authored-by: 이지은 <ijieun@ijieun-ui-MacBookPro.local>

src/routes/message/+page.svelte

@@ -0,0 +1,29 @@
+<script>
+	import Header from '$lib/components/ui/Header.svelte';
+	import Artwork from '$lib/components/ui/Artwork/Artwork.svelte';
+	import MessageForm from '$lib/components/ui/message/MessageForm.svelte';
+
+	let message = $state('');
+
+	const artworkTitle = $derived(message ? 'Your message' : 'Title');
+
+	const artworkDescription = $derived(message || 'Description Description Description');
+</script>
+
+<!--
+	create / upload와 같은 2열 레이아웃.
+	우측 MessageForm에서 프리셋 메시지를 pill 버튼으로 선택합니다.
+-->
+<div
+	class="flex h-dvh flex-col overflow-x-hidden bg-surface text-ink lg:h-screen lg:overflow-hidden"
+>
+	<Header step={4} total={6} />
+
+	<main class="flex min-h-0 flex-1 flex-col lg:flex-row">
+		<Artwork title={artworkTitle} description={artworkDescription} />
+
+		<section class="relative flex min-h-0 flex-1 flex-col lg:overflow-y-auto">
+			<MessageForm bind:message />
+		</section>
+	</main>
+</div>