feat: add PDF annotation feature (#40)

Backend:
- Add ANNOTATE_ALL permission
- Add ANNOTATION_NOT_FOUND and ANNOTATION_OVERLAP error codes
- V10 migration: document_annotations table with page/rect/color/owner
- DocumentAnnotation entity, AnnotationRepository, CreateAnnotationDTO
- AnnotationService: overlap detection (rectangle intersection), ownership enforcement on delete
- AnnotationController: GET (authenticated), POST/DELETE (ANNOTATE_ALL)
- 15 new tests (AnnotationServiceTest, AnnotationControllerTest) — TDD red/green

Frontend:
- AnnotationLayer.svelte: pointer-event drawing, colored rect overlays, delete buttons
- PdfViewer.svelte: annotate toggle, color picker, loads/saves/deletes annotations via API
- Disabled annotate button with tooltip for users without ANNOTATE_ALL
- canAnnotate exposed from layout server, passed to PdfViewer
- errors.ts + de/en/es translations for new error codes
- 3 new unit tests for AnnotationLayer — TDD red/green

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

frontend/src/lib/components/PdfViewer.svelte

@@ -1,8 +1,17 @@
 <script lang="ts">
 import { onMount } from 'svelte';
 import type { PDFDocumentProxy, PDFPageProxy, RenderTask } from 'pdfjs-dist';
+import AnnotationLayer from './AnnotationLayer.svelte';
 
-let { url }: { url: string } = $props();
+let {
+	url,
+	documentId = '',
+	canAnnotate = false
+}: {
+	url: string;
+	documentId?: string;
+	canAnnotate?: boolean;
+} = $props();
 
 let pdfDoc = $state<PDFDocumentProxy | null>(null);
 let currentPage = $state(1);
@@ -24,6 +33,22 @@ let textLayerInstance: { cancel: () => void } | null = null;
 let pdfjsLib: typeof import('pdfjs-dist') | null = null;
 let pdfjsReady = $state(false);
 
+type Annotation = {
+	id: string;
+	documentId: string;
+	pageNumber: number;
+	x: number;
+	y: number;
+	width: number;
+	height: number;
+	color: string;
+	createdAt: string;
+};
+
+let annotations = $state<Annotation[]>([]);
+let annotateMode = $state(false);
+let annotateColor = $state('#ffff00');
+
 onMount(async () => {
 	// Dynamic import keeps pdfjs out of the SSR bundle entirely
 	const [lib, { default: workerUrl }] = await Promise.all([
@@ -134,6 +159,54 @@ async function prerender(doc: PDFDocumentProxy, pageNum: number) {
 	}
 }
 
+async function loadAnnotations(docId: string) {
+	if (!docId) return;
+	try {
+		const res = await fetch(`/api/documents/${docId}/annotations`);
+		if (res.ok) annotations = await res.json();
+	} catch {
+		// ignore
+	}
+}
+
+async function handleAnnotationDraw(rect: { x: number; y: number; width: number; height: number }) {
+	if (!documentId) return;
+	try {
+		const res = await fetch(`/api/documents/${documentId}/annotations`, {
+			method: 'POST',
+			headers: { 'Content-Type': 'application/json' },
+			body: JSON.stringify({
+				pageNumber: currentPage,
+				x: rect.x,
+				y: rect.y,
+				width: rect.width,
+				height: rect.height,
+				color: annotateColor
+			})
+		});
+		if (res.ok) {
+			const created: Annotation = await res.json();
+			annotations = [...annotations, created];
+		}
+	} catch {
+		// ignore
+	}
+}
+
+async function handleAnnotationDelete(annotationId: string) {
+	if (!documentId) return;
+	try {
+		const res = await fetch(`/api/documents/${documentId}/annotations/${annotationId}`, {
+			method: 'DELETE'
+		});
+		if (res.ok) {
+			annotations = annotations.filter((a) => a.id !== annotationId);
+		}
+	} catch {
+		// ignore
+	}
+}
+
 $effect(() => {
 	if (pdfjsReady && url) {
 		loadDocument(url);
@@ -151,6 +224,12 @@ $effect(() => {
 	}
 });
 
+$effect(() => {
+	if (documentId) {
+		loadAnnotations(documentId);
+	}
+});
+
 function prevPage() {
 	if (currentPage > 1) currentPage -= 1;
 }
@@ -274,6 +353,37 @@ function zoomOut() {
 					</svg>
 				</button>
 			</div>
+
+			<!-- Annotate controls -->
+			{#if canAnnotate}
+				<div class="flex items-center gap-1">
+					<button
+						onclick={() => (annotateMode = !annotateMode)}
+						aria-label={annotateMode ? 'Annotieren beenden' : 'Annotieren'}
+						class="rounded px-2 py-1 font-sans text-xs text-gray-300 transition hover:bg-white/10 {annotateMode ? 'bg-white/20' : ''}"
+					>
+						{annotateMode ? 'Fertig' : 'Annotieren'}
+					</button>
+					{#if annotateMode}
+						<input
+							type="color"
+							bind:value={annotateColor}
+							aria-label="Farbe wählen"
+							class="h-6 w-6 cursor-pointer rounded border-0 bg-transparent p-0"
+							title="Farbe wählen"
+						/>
+					{/if}
+				</div>
+			{:else}
+				<button
+					disabled
+					title="Sie benötigen die Berechtigung ANNOTATE_ALL zum Annotieren"
+					class="cursor-not-allowed rounded px-2 py-1 font-sans text-xs text-gray-500"
+					aria-label="Annotieren (keine Berechtigung)"
+				>
+					Annotieren
+				</button>
+			{/if}
 		</div>
 
 		<!-- PDF canvas area -->
@@ -297,6 +407,13 @@ function zoomOut() {
 							class="textLayer"
 							style="position: absolute; top: 0; left: 0; overflow: hidden; pointer-events: none; line-height: 1;"
 						></div>
+						<AnnotationLayer
+							annotations={annotations.filter((a) => a.pageNumber === currentPage)}
+							canAnnotate={annotateMode}
+							color={annotateColor}
+							onDraw={handleAnnotationDraw}
+							onDelete={handleAnnotationDelete}
+						/>
 					</div>
 				</div>
 			{/if}