feat(frontend): unify page shell and move create flows to dedicated routes

frontend/src/lib/components/PageHeader.svelte

@@ -0,0 +1,62 @@
+<script lang="ts">
+	import type { Snippet } from 'svelte';
+	import { ArrowLeft } from 'lucide-svelte';
+
+	let {
+		title,
+		kicker,
+		subtitle,
+		backHref,
+		backLabel,
+		className = '',
+		titleClassName = 'editorial-title',
+		meta,
+		actions,
+		children
+	}: {
+		title: string;
+		kicker?: string;
+		subtitle?: string;
+		backHref?: string;
+		backLabel?: string;
+		className?: string;
+		titleClassName?: string;
+		meta?: Snippet;
+		actions?: Snippet;
+		children?: Snippet;
+	} = $props();
+</script>
+
+<section class={`editorial-hero reveal-1 ${className}`.trim()}>
+	{#if backHref && backLabel}
+		<a href={backHref} class="editorial-backlink"><ArrowLeft class="size-4" /> {backLabel}</a>
+	{/if}
+
+	{#if kicker}
+		<p class="editorial-kicker">{kicker}</p>
+	{/if}
+
+	<h1 class={titleClassName}>{title}</h1>
+
+	{#if subtitle}
+		<p class="editorial-subtitle">{subtitle}</p>
+	{/if}
+
+	{#if meta}
+		<div class="page-header-meta">
+			{@render meta()}
+		</div>
+	{/if}
+
+	{#if actions}
+		<div class="editorial-toolbar">
+			{@render actions()}
+		</div>
+	{/if}
+
+	{#if children}
+		<div class="page-header-foot">
+			{@render children()}
+		</div>
+	{/if}
+</section>