Rebuild admin pages around DataTable/AdminModal; restructure categories/groups and v2 groups API

Remove the generic $lib/svelte-admin CRUD layer and AdminTable.svelte; each
admin route now owns its own form/modal logic. Add DataTable.svelte,
superform-errors.ts, and profile-specific modal/field components.

Flatten proclamation categories/groups and drop subscription levels; add the
v2 groups API; update v1/v2 endpoints, serializers, auth, and regenerated
Prisma client with the new migrations.

Document the overhaul plan in docs/ADMIN_OVERHAUL.md.

src/routes/+page.svelte

@@ -1,3 +1,41 @@
-<div class="flex flex-1 flex-col items-center justify-center">
-	<h1 class="dark:text-gray-100">Hello</h1>
-</div>
+<script lang="ts">
+	import { authClient } from '$lib/auth-client';
+	import { resolve } from '$app/paths';
+
+	const session = authClient.useSession();
+	const signedIn = $derived(!!$session.data?.user);
+</script>
+
+<section class="py-16 sm:py-24">
+	<div class="mx-auto w-full max-w-6xl px-4">
+		<div class="mx-auto flex max-w-3xl flex-col items-center text-center">
+			<h1 class="mt-6 text-4xl font-bold tracking-tight text-slate-900 sm:text-5xl">
+				Welcome to the Radiant Wave Portal
+			</h1>
+
+			<div class="mt-8 flex flex-col items-center gap-3 sm:flex-row">
+				{#if signedIn}
+					<a
+						href={resolve('/dashboard')}
+						class="inline-flex h-12 items-center justify-center rounded-lg bg-indigo-600 px-8 text-base font-medium text-white shadow-sm transition hover:bg-indigo-700"
+					>
+						Go to Dashboard
+					</a>
+				{:else}
+					<a
+						href={resolve('/login')}
+						class="inline-flex h-12 w-full items-center justify-center rounded-lg bg-indigo-600 px-8 text-base font-medium text-white shadow-sm transition hover:bg-indigo-700 sm:w-auto"
+					>
+						Get Started
+					</a>
+					<a
+						href={resolve('/register')}
+						class="inline-flex h-12 w-full items-center justify-center rounded-lg border border-slate-300 bg-white px-8 text-base font-medium text-slate-700 transition hover:bg-slate-50 sm:w-auto"
+					>
+						Create Account
+					</a>
+				{/if}
+			</div>
+		</div>
+	</div>
+</section>