feat(frontend): hide outdated annotations when file version changes

- Regenerate API types with fileHash on Document and DocumentAnnotation
- PdfViewer accepts documentFileHash prop; filters visibleAnnotations to
  those whose hash matches (or is null) and shows an amber notice banner
  when any annotations are hidden due to a hash mismatch
- Document detail page passes doc.fileHash to PdfViewer
- Add i18n key annotation_outdated_notice in de/en/es
- E2E: two new tests covering hide-on-reupload and restore-on-original-reupload
  scenarios; add minimal2.pdf fixture for a different-hash upload

Closes #55

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

frontend/src/lib/components/PdfViewer.svelte

@@ -4,6 +4,7 @@ import { SvelteMap } from 'svelte/reactivity';
 import type { PDFDocumentProxy, PDFPageProxy, RenderTask } from 'pdfjs-dist';
 import AnnotationLayer from './AnnotationLayer.svelte';
 import AnnotationCommentPanel from './AnnotationCommentPanel.svelte';
+import { m } from '$lib/paraglide/messages.js';
 
 let {
 	url,
@@ -11,7 +12,8 @@ let {
 	canAnnotate = false,
 	canComment,
 	currentUserId,
-	canAdmin
+	canAdmin,
+	documentFileHash
 }: {
 	url: string;
 	documentId?: string;
@@ -19,6 +21,7 @@ let {
 	canComment?: boolean;
 	currentUserId?: string | null;
 	canAdmin?: boolean;
+	documentFileHash?: string | null;
 } = $props();
 
 let pdfDoc = $state<PDFDocumentProxy | null>(null);
@@ -51,6 +54,7 @@ type Annotation = {
 	height: number;
 	color: string;
 	createdAt: string;
+	fileHash?: string | null;
 };
 
 let annotations = $state<Annotation[]>([]);
@@ -59,6 +63,11 @@ let annotateColor = $state('#ffff00');
 let commentCounts = new SvelteMap<string, number>();
 let activeAnnotationId = $state<string | null>(null);
 
+const visibleAnnotations = $derived(
+	annotations.filter((a) => !a.fileHash || !documentFileHash || a.fileHash === documentFileHash)
+);
+const outdatedCount = $derived(annotations.length - visibleAnnotations.length);
+
 onMount(async () => {
 	// Dynamic import keeps pdfjs out of the SSR bundle entirely
 	const [lib, { default: workerUrl }] = await Promise.all([
@@ -298,6 +307,27 @@ function zoomOut() {
 	</div>
 {:else}
 	<div class="flex h-full w-full flex-col bg-[#2A2A2A]">
+		{#if outdatedCount > 0}
+			<div
+				class="flex shrink-0 items-center gap-2 border-b border-amber-500/30 bg-amber-500/10 px-4 py-2"
+				data-testid="annotation-outdated-notice"
+			>
+				<svg
+					class="h-4 w-4 shrink-0 text-amber-400"
+					viewBox="0 0 24 24"
+					fill="none"
+					stroke="currentColor"
+					stroke-width="2"
+				>
+					<path
+						stroke-linecap="round"
+						stroke-linejoin="round"
+						d="M12 9v3.75m-9.303 3.376c-.866 1.5.217 3.374 1.948 3.374h14.71c1.73 0 2.813-1.874 1.948-3.374L13.949 3.378c-.866-1.5-3.032-1.5-3.898 0L2.697 16.126zM12 15.75h.007v.008H12v-.008z"
+					/>
+				</svg>
+				<span class="font-sans text-xs text-amber-300">{m.annotation_outdated_notice()}</span>
+			</div>
+		{/if}
 		<!-- Controls -->
 		<div
 			class="flex shrink-0 items-center justify-between gap-2 border-b border-white/10 px-4 py-2"
@@ -439,7 +469,7 @@ function zoomOut() {
 							style="position: absolute; top: 0; left: 0; overflow: hidden; pointer-events: none; line-height: 1;"
 						></div>
 						<AnnotationLayer
-							annotations={annotations.filter((a) => a.pageNumber === currentPage)}
+							annotations={visibleAnnotations.filter((a) => a.pageNumber === currentPage)}
 							canAnnotate={annotateMode}
 							color={annotateColor}
 							onDraw={handleAnnotationDraw}