feat(documents): add delete button to document edit form

- DELETE /api/documents/{id} endpoint (204 No Content, WRITE_ALL required)
- DocumentService.deleteDocument() — throws 404 if not found, cascades
  via DB foreign keys (versions, annotations, comments all ON DELETE CASCADE)
- Delete form action in edit page server: redirects to / on success
- Two-step confirmation in the save bar: first click reveals inline
  "Wirklich löschen?" + confirm/cancel, avoiding native browser dialogs
- i18n key doc_delete_confirm added to de/en/es

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

frontend/src/routes/documents/[id]/edit/+page.server.ts

@@ -58,5 +58,20 @@ export const actions = {
 		}
 
 		throw redirect(303, `/documents/${params.id}`);
+	},
+
+	delete: async ({ params, fetch }) => {
+		const baseUrl = env.API_INTERNAL_URL || 'http://localhost:8080';
+
+		const res = await fetch(`${baseUrl}/api/documents/${params.id}`, {
+			method: 'DELETE'
+		});
+
+		if (!res.ok) {
+			const backendError = await parseBackendError(res);
+			return fail(res.status, { error: getErrorMessage(backendError?.code) });
+		}
+
+		throw redirect(303, '/');
 	}
 };

frontend/src/routes/documents/[id]/edit/+page.svelte

@@ -17,6 +17,7 @@ let selectedReceivers = $state(doc.receivers ?? []);
 let dateDisplay = $state(isoToGerman(doc.documentDate ?? ''));
 let dateIso = $state(doc.documentDate ?? '');
 let dateDirty = $state(false);
+let confirmDelete = $state(false);
 
 const dateInvalid = $derived(dateDirty && dateDisplay.length > 0 && dateIso === '');
 
@@ -244,18 +245,58 @@ function handleDateInput(e: Event) {
 		<div
 			class="sticky bottom-0 z-10 -mx-4 flex items-center justify-between border-t border-line bg-surface px-6 py-4 shadow-[0_-2px_8px_rgba(0,0,0,0.06)]"
 		>
-			<a
-				href="/documents/{doc.id}"
-				class="text-sm font-medium text-ink-2 transition-colors hover:text-ink"
-			>
-				{m.btn_cancel()}
-			</a>
-			<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"
-			>
-				{m.btn_save()}
-			</button>
+			<!-- Left: delete -->
+			<div class="flex items-center gap-3">
+				{#if confirmDelete}
+					<span class="font-sans text-sm text-red-700">{m.doc_delete_confirm()}</span>
+					<button
+						type="submit"
+						form="delete-form"
+						class="rounded bg-red-600 px-4 py-1.5 text-sm font-bold text-white transition-colors hover:bg-red-700"
+					>
+						{m.btn_delete()}
+					</button>
+					<button
+						type="button"
+						onclick={() => (confirmDelete = false)}
+						class="text-sm text-ink-2 transition-colors hover:text-ink"
+					>
+						{m.btn_cancel()}
+					</button>
+				{:else}
+					<button
+						type="button"
+						onclick={() => (confirmDelete = true)}
+						class="flex items-center gap-1.5 text-sm text-ink-3 transition-colors hover:text-red-600"
+					>
+						<img
+							src="/degruyter-icons/Simple/Medium-24px/SVG/Action/Delete/Delete-MD.svg"
+							alt=""
+							aria-hidden="true"
+							class="h-4 w-4"
+						/>
+						{m.btn_delete()}
+					</button>
+				{/if}
+			</div>
+
+			<!-- Right: cancel + save -->
+			<div class="flex items-center gap-4">
+				<a
+					href="/documents/{doc.id}"
+					class="text-sm font-medium text-ink-2 transition-colors hover:text-ink"
+				>
+					{m.btn_cancel()}
+				</a>
+				<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"
+				>
+					{m.btn_save()}
+				</button>
+			</div>
 		</div>
 	</form>
+
+	<form id="delete-form" method="POST" action="?/delete" use:enhance></form>
 </div>