fix(enrich): use fixed positioning for fullscreen layout and fix done icon

Align enrich/[id] with the document detail page pattern: position fixed
with runtime header height measurement instead of a hardcoded calc value.
The root layout is reverted to its original simple form with no per-route
detection. Also replaces the missing check icon on the done page with
Check-Double-LG from the icon library.

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

frontend/src/routes/enrich/[id]/+page.svelte

@@ -1,6 +1,6 @@
 <script lang="ts">
 import { enhance } from '$app/forms';
-import { untrack } from 'svelte';
+import { onMount, untrack } from 'svelte';
 import { m } from '$lib/paraglide/messages.js';
 import DocumentViewer from '$lib/components/DocumentViewer.svelte';
 import WhoWhenSection from '$lib/components/document/WhoWhenSection.svelte';
@@ -15,6 +15,11 @@ let fileUrl = $state('');
 let fileError = $state('');
 let isLoading = $state(false);
 
+let navHeight = $state(0);
+onMount(() => {
+	navHeight = document.querySelector('header')?.getBoundingClientRect().height ?? 0;
+});
+
 // Dummy bindable state required by DocumentViewer
 let annotateMode = $state(false);
 let activeAnnotationId = $state<string | null>(null);
@@ -52,7 +57,7 @@ let selectedReceivers = $state(untrack(() => doc.receivers ?? []));
 	<title>{doc.title || doc.originalFilename || 'Dokument'} — Anreicherung</title>
 </svelte:head>
 
-<div class="flex h-[calc(100vh-68px)] flex-col">
+<div class="fixed inset-x-0 bottom-0 flex flex-col" style="top: {navHeight}px">
 	<!-- Top bar -->
 	<div class="flex items-center justify-between border-b border-line bg-surface px-6 py-3">
 		<a

frontend/src/routes/enrich/done/+page.svelte

@@ -7,7 +7,7 @@ import { m } from '$lib/paraglide/messages.js';
 		class="border-brand-sand flex flex-col items-center justify-center rounded-sm border bg-white py-20 text-center shadow-sm"
 	>
 		<img
-			src="/degruyter-icons/Simple/Large-32px/SVG/Action/Check/Check-Circle-LG.svg"
+			src="/degruyter-icons/Simple/Large-32px/SVG/Action/Check/Check-Double-LG.svg"
 			alt=""
 			aria-hidden="true"
 			class="mb-6 h-16 w-16"