fix(security): add csrfFetch wrapper and apply to all client-side mutating requests

Introduces `csrfFetch` (= `makeCsrfFetch(fetch)`) in cookies.ts as a
drop-in fetch replacement that auto-injects X-XSRF-TOKEN on POST/PUT/PATCH/DELETE.

Previously 8 call sites sent mutating requests without the CSRF header —
annotation resize, comment POST/PATCH/DELETE, Geschichte CRUD, Stammbaum
relationship creation, bulk-edit PATCH, and file upload — all would fail
with CSRF_TOKEN_MISSING if the backend's cookie-based protection triggered.

All 14 client-side mutating fetches now use csrfFetch; withCsrf/makeCsrfFetch
remain in the API for injectable-fetch use cases (e.g. useTranscriptionBlocks).

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

frontend/src/lib/document/BulkDocumentEditLayout.svelte

@@ -17,7 +17,7 @@ import PdfViewer from '$lib/document/viewer/PdfViewer.svelte';
 import { bulkTitleFromFilename } from '$lib/document/filename';
 import type { Tag } from '$lib/tag/TagInput.svelte';
 import type { components } from '$lib/generated/api';
-import { withCsrf } from '$lib/shared/cookies';
+import { csrfFetch } from '$lib/shared/cookies';
 
 type Person = components['schemas']['Person'];
 
@@ -184,10 +184,10 @@ async function saveUpload() {
 		// FormData with per-chunk progress. Session cookie is sent automatically
 		// by the browser for same-origin requests.
 		try {
-			const res = await fetch(
-				'/api/documents/quick-upload',
-				withCsrf({ method: 'POST', body: formData })
-			);
+			const res = await csrfFetch('/api/documents/quick-upload', {
+				method: 'POST',
+				body: formData
+			});
 			const body = await res.json().catch(() => ({ errors: [] }));
 			const errorFilenames = new Set<string>(
 				(body.errors ?? []).map((err: { filename: string }) => err.filename)
@@ -241,7 +241,7 @@ async function saveBulkEdit() {
 	for (let i = 0; i < chunks.length; i++) {
 		const chunk = chunks[i];
 		try {
-			const res = await fetch('/api/documents/bulk', {
+			const res = await csrfFetch('/api/documents/bulk', {
 				method: 'PATCH',
 				headers: { 'Content-Type': 'application/json' },
 				body: JSON.stringify({ ...dto, documentIds: chunk })

frontend/src/lib/document/DocumentEditLayout.svelte

@@ -13,6 +13,7 @@ import WhoWhenSection from '$lib/document/WhoWhenSection.svelte';
 import DescriptionSection from '$lib/document/DescriptionSection.svelte';
 import type { Tag } from '$lib/tag/TagInput.svelte';
 import type { components } from '$lib/generated/api';
+import { csrfFetch } from '$lib/shared/cookies';
 import type { DatePrecision } from '$lib/shared/utils/documentDate';
 
 type Person = components['schemas']['Person'];
@@ -86,7 +87,7 @@ async function handleFile(file: File) {
 	try {
 		const formData = new FormData();
 		formData.append('file', file);
-		const res = await fetch(`/api/documents/${doc.id}/file`, {
+		const res = await csrfFetch(`/api/documents/${doc.id}/file`, {
 			method: 'POST',
 			body: formData,
 			signal: controller.signal

frontend/src/lib/document/transcription/TranscriptionEditView.svelte

@@ -6,7 +6,7 @@ import TranscribeCoachEmptyState from '$lib/shared/help/TranscribeCoachEmptyStat
 import type { PersonMention, TranscriptionBlockData } from '$lib/shared/types';
 import { createBlockAutoSave } from '$lib/document/transcription/useBlockAutoSave.svelte';
 import { createBlockDragDrop } from '$lib/document/transcription/useBlockDragDrop.svelte';
-import { withCsrf } from '$lib/shared/cookies';
+import { csrfFetch } from '$lib/shared/cookies';
 
 type Props = {
 	documentId: string;
@@ -114,14 +114,11 @@ function handleDelete(blockId: string) {
 
 async function reorder(newOrder: string[]) {
 	try {
-		const res = await fetch(
-			`/api/documents/${documentId}/transcription-blocks/reorder`,
-			withCsrf({
-				method: 'PUT',
-				headers: { 'Content-Type': 'application/json' },
-				body: JSON.stringify({ blockIds: newOrder })
-			})
-		);
+		const res = await csrfFetch(`/api/documents/${documentId}/transcription-blocks/reorder`, {
+			method: 'PUT',
+			headers: { 'Content-Type': 'application/json' },
+			body: JSON.stringify({ blockIds: newOrder })
+		});
 		if (!res.ok) return;
 		const updated = await res.json();
 		for (const b of updated) {

frontend/src/lib/document/transcription/useBlockAutoSave.svelte.ts

@@ -1,6 +1,6 @@
 import { SvelteMap } from 'svelte/reactivity';
 import type { PersonMention } from '$lib/shared/types';
-import { withCsrf } from '$lib/shared/cookies';
+import { csrfFetch } from '$lib/shared/cookies';
 
 export type SaveState = 'idle' | 'saving' | 'saved' | 'fading' | 'error';
 
@@ -117,15 +117,12 @@ export function createBlockAutoSave({ saveFn, documentId }: Options) {
 		for (const [blockId, text] of pendingTexts) {
 			const mentions = pendingMentions.get(blockId) ?? [];
 			clearDebounce(blockId);
-			void fetch(
-				`/api/documents/${documentId}/transcription-blocks/${blockId}`,
-				withCsrf({
-					method: 'PUT',
-					headers: { 'Content-Type': 'application/json' },
-					body: JSON.stringify({ text, mentionedPersons: mentions }),
-					keepalive: true
-				})
-			);
+			void csrfFetch(`/api/documents/${documentId}/transcription-blocks/${blockId}`, {
+				method: 'PUT',
+				headers: { 'Content-Type': 'application/json' },
+				body: JSON.stringify({ text, mentionedPersons: mentions }),
+				keepalive: true
+			});
 			pendingTexts.delete(blockId);
 			pendingMentions.delete(blockId);
 		}

frontend/src/lib/document/viewer/PdfViewer.svelte

@@ -6,6 +6,7 @@ import AnnotationLayer from '$lib/document/annotation/AnnotationLayer.svelte';
 import type { Annotation } from '$lib/shared/types';
 import { m } from '$lib/paraglide/messages.js';
 import { parseBackendError, getErrorMessage } from '$lib/shared/errors';
+import { csrfFetch } from '$lib/shared/cookies';
 
 type DrawRect = { x: number; y: number; width: number; height: number; pageNumber: number };
 
@@ -132,7 +133,7 @@ async function updateAnnotation(
 	coords: { x: number; y: number; width: number; height: number }
 ) {
 	if (!documentId) return;
-	const res = await fetch(`/api/documents/${documentId}/annotations/${annotationId}`, {
+	const res = await csrfFetch(`/api/documents/${documentId}/annotations/${annotationId}`, {
 		method: 'PATCH',
 		headers: { 'Content-Type': 'application/json' },
 		body: JSON.stringify(coords)