feat: add upload page UI (moodboard + SNS feed)

* feat: add upload page initial UI

* feat: add moodboard and SNS feed upload layouts

* fix: improve mobile upload page layout

src/lib/components/ui/upload/SnsFeedUpload.svelte

@@ -0,0 +1,45 @@
+<script>
+	import UploadTile from './UploadTile.svelte';
+
+	// Two SNS feed screenshots. On desktop they fill the panel edge-to-edge in
+	// a staggered composition (one raised on the right, one dropped on the
+	// left); below that they fall back to a simple side-by-side / stacked grid.
+</script>
+
+<div class="feed w-full min-h-0 flex-1">
+	<UploadTile class="tile-one h-full min-h-0 w-full max-lg:aspect-auto lg:aspect-auto aspect-4/5" />
+	<UploadTile class="tile-two h-full min-h-0 w-full max-lg:aspect-auto lg:aspect-auto aspect-4/5" />
+</div>
+
+<style>
+	.feed {
+		display: grid;
+		gap: 0;
+		grid-template-columns: 1fr 1fr;
+		grid-template-rows: 1fr;
+		width: 100%;
+		flex: 1;
+		min-height: 0;
+	}
+
+	@media (min-width: 1024px) {
+		.feed {
+			grid-template-rows: repeat(5, 1fr);
+			grid-template-areas:
+				'.   two'
+				'one two'
+				'one two'
+				'one two'
+				'one .';
+			min-height: 34rem;
+		}
+
+		:global(.tile-one) {
+			grid-area: one;
+		}
+
+		:global(.tile-two) {
+			grid-area: two;
+		}
+	}
+</style>