feat(enrich): add metadata enrichment queue UI

Home page shows "Needs metadata" card when incomplete documents exist.
/enrich list shows all incomplete documents; /enrich/[id] provides a
split PDF-preview + compact form view with Skip / Save / Save & reviewed
actions that auto-advance through the queue.

New document page gets Save vs Save & reviewed split. Edit page gets
"Mark for review" secondary button to push a document back into the queue.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/routes/documents/[id]/edit/SaveBar.svelte

@@ -1,5 +1,6 @@
 <script lang="ts">
 import { m } from '$lib/paraglide/messages.js';
+import { enhance } from '$app/forms';
 
 let { docId }: { docId: string } = $props();
 
@@ -54,7 +55,7 @@ let confirmDelete = $state(false);
 		{/if}
 	</div>
 
-	<!-- Right: cancel + save -->
+	<!-- Right: cancel + mark for review + save -->
 	<div class="flex items-center gap-4">
 		<a
 			href="/documents/{docId}"
@@ -62,6 +63,13 @@ let confirmDelete = $state(false);
 		>
 			{m.btn_cancel()}
 		</a>
+		<button
+			type="submit"
+			form="mark-for-review-form"
+			class="rounded-sm border border-gray-300 px-4 py-2 font-sans text-xs font-bold tracking-widest text-gray-600 uppercase transition-colors hover:bg-gray-50"
+		>
+			{m.btn_mark_for_review()}
+		</button>
 		<button
 			type="submit"
 			class="rounded bg-primary px-6 py-2 text-sm font-bold tracking-widest text-white uppercase transition-colors hover:bg-primary/80"
@@ -70,3 +78,5 @@ let confirmDelete = $state(false);
 		</button>
 	</div>
 </div>
+
+<form id="mark-for-review-form" method="POST" action="?/markForReview" use:enhance></form>