feat(persons): add /persons/[id]/edit route with PersonEditForm, PersonDangerZone

New edit route with WRITE_ALL guard; PersonEditForm (6 fields), sticky
PersonEditSaveBar, collapsed PersonDangerZone with PersonMergePanel.

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

frontend/src/routes/persons/[id]/edit/PersonDangerZone.svelte

@@ -0,0 +1,44 @@
+<script lang="ts">
+import { m } from '$lib/paraglide/messages.js';
+import PersonMergePanel from '../PersonMergePanel.svelte';
+
+let {
+	person,
+	form
+}: {
+	person: { id: string; firstName: string; lastName: string };
+	form?: { mergeError?: string } | null;
+} = $props();
+
+let open = $state(false);
+</script>
+
+<div class="mt-8 overflow-hidden rounded-sm border border-red-200 bg-surface shadow-sm">
+	<button
+		type="button"
+		onclick={() => (open = !open)}
+		class="flex w-full items-center justify-between px-6 py-4 text-left"
+		aria-expanded={open}
+	>
+		<span class="text-sm font-bold tracking-widest text-red-600 uppercase">
+			{m.person_danger_zone_heading()}
+		</span>
+		<svg
+			class="h-4 w-4 text-red-400 transition-transform {open ? 'rotate-180' : ''}"
+			fill="none"
+			stroke="currentColor"
+			viewBox="0 0 24 24"
+			aria-hidden="true"
+		>
+			<path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M19 9l-7 7-7-7" />
+		</svg>
+	</button>
+
+	{#if open}
+		<div class="border-t border-red-100 px-6 py-4">
+			{#key person.id}
+				<PersonMergePanel person={person} form={form} />
+			{/key}
+		</div>
+	{/if}
+</div>