refactor(nav): replace static back-link hrefs with BackButton

All 7 in-scope back navigation links converted to use history.back().
Admin panel mobile chevron converted inline (icon-only, different
visual pattern). Cancel buttons left as static <a> links.

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

frontend/src/routes/persons/new/+page.svelte

@@ -1,30 +1,13 @@
 <script lang="ts">
 import { m } from '$lib/paraglide/messages.js';
+import BackButton from '$lib/components/BackButton.svelte';
 let { form } = $props();
 </script>
 
 <div class="mx-auto max-w-2xl px-4 py-8">
 	<!-- Heading -->
 	<div class="mb-6">
-		<a
-			href="/persons"
-			class="group mb-4 inline-flex items-center text-xs font-bold tracking-widest text-ink-2 uppercase transition-colors hover:text-ink"
-		>
-			<svg
-				class="mr-2 h-4 w-4 transform transition-transform group-hover:-translate-x-1"
-				fill="none"
-				stroke="currentColor"
-				viewBox="0 0 24 24"
-			>
-				<path
-					stroke-linecap="round"
-					stroke-linejoin="round"
-					stroke-width="2"
-					d="M10 19l-7-7m0 0l7-7m-7 7h18"
-				/>
-			</svg>
-			{m.btn_back_to_overview()}
-		</a>
+		<BackButton />
 		<h1 class="font-serif text-3xl text-ink">{m.persons_new_heading()}</h1>
 	</div>