feat(geschichten): add /geschichten routes (index, detail, new, edit)

- /geschichten — published-stories index with filter pills + "+ Neue Geschichte"
  for BLOG_WRITERs; supports ?personId and ?documentId pre-filtering
- /geschichten/[id] — reader detail with sanitised {@html} body, person and
  document chip sections, BLOG_WRITER edit/delete with confirm dialog
- /geschichten/new — editor with optional ?personId and ?documentId pre-fill
  (silent ignore on unknown IDs to avoid leaking entity existence)
- /geschichten/[id]/edit — editor populated from existing story; BLOG_WRITE
  guard redirects readers to the detail page

All routes load via createApiClient(fetch) with !response.ok error handling
following the project pattern; PATCH/DELETE go through raw fetch which the
Vite dev proxy / Caddy production proxy authenticates via cookie.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

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

@@ -0,0 +1,60 @@
+<script lang="ts">
+import { goto } from '$app/navigation';
+import { m } from '$lib/paraglide/messages.js';
+import GeschichteEditor from '$lib/components/GeschichteEditor.svelte';
+import BackButton from '$lib/components/BackButton.svelte';
+import { getErrorMessage } from '$lib/errors';
+import type { PageData } from './$types';
+
+let { data }: { data: PageData } = $props();
+
+let submitting = $state(false);
+let errorMessage: string | null = $state(null);
+
+async function handleSubmit(payload: {
+	title: string;
+	body: string;
+	status: 'DRAFT' | 'PUBLISHED';
+	personIds: string[];
+	documentIds: string[];
+}) {
+	submitting = true;
+	errorMessage = null;
+	try {
+		const res = await fetch(`/api/geschichten/${data.geschichte.id}`, {
+			method: 'PATCH',
+			headers: { 'Content-Type': 'application/json' },
+			body: JSON.stringify(payload)
+		});
+		if (!res.ok) {
+			const code = (await res.json().catch(() => ({})))?.code;
+			errorMessage = getErrorMessage(code);
+			return;
+		}
+		goto(`/geschichten/${data.geschichte.id}`);
+	} finally {
+		submitting = false;
+	}
+}
+</script>
+
+<div class="mx-auto max-w-5xl px-4 py-8">
+	<div class="mb-6">
+		<BackButton />
+	</div>
+
+	<h1 class="mb-6 font-serif text-3xl font-bold text-ink">
+		{m.btn_edit()}: {data.geschichte.title}
+	</h1>
+
+	{#if errorMessage}
+		<div
+			class="mb-4 rounded border border-danger bg-danger/10 p-3 text-sm text-danger"
+			role="alert"
+		>
+			{errorMessage}
+		</div>
+	{/if}
+
+	<GeschichteEditor geschichte={data.geschichte} onSubmit={handleSubmit} submitting={submitting} />
+</div>