fix some signup ux issues

frontend/src/routes/[fam]/[username]/+page.svelte

@@ -911,6 +911,9 @@
 		<p class="empty">Loading...</p>
 	{:else if error}
 		<p class="error">{error}</p>
+		<p class="empty">
+			<Button href={`/${famSlug}/join/${username}`} variant="primary" size="md">Join</Button>
+		</p>
 	{:else}
 		{#if simulateEow}
 			<div class="preview-notice">

frontend/src/routes/[fam]/[username]/settings/+page.svelte

@@ -82,7 +82,7 @@
 	let copied = $state(false);
 	let parentInviteEmail = $state('');
 
-	let members = $state(famStore.initialized ? famStore.members : data.members || []);
+	let members = $derived(famStore.initialized ? famStore.members : (data.members || []));
 	let deletingSeason = $state<any>(null);
 	let issued = $state<{ otp: string; joinUrl: string; name: string } | null>(null);
 

frontend/src/routes/[fam]/join/+page.server.ts

@@ -0,0 +1,33 @@
+import { fail, redirect } from '@sveltejs/kit';
+import { redeemOtp } from '$lib/server/member-otp';
+import { handle } from '@shared/slugify';
+import { setSessionCookie, clearLegacyCookies } from '$lib/server/session';
+
+export const actions = {
+	default: async (event) => {
+		const fam = event.params.fam;
+		const fd = await event.request.formData();
+		const name = (fd.get('name') || '').toString().trim();
+		const otp = (fd.get('otp') || '').toString().trim();
+
+		if (!name) return fail(400, { error: 'Enter your name.', name, otp });
+		if (!otp) return fail(400, { error: 'Enter the code shown by your parent.', name, otp });
+
+		try {
+			// redeemOtp derives the username from the handle internally; pass the
+			// raw name so it resolves the same {famSlug}:{handle} identity.
+			const token = await redeemOtp({ famSlug: fam, username: name, otp });
+			clearLegacyCookies(event.cookies);
+			setSessionCookie(event.cookies, token);
+		} catch (e) {
+			return fail(400, {
+				error: e instanceof Error ? e.message : 'Join failed',
+				name,
+				otp
+			});
+		}
+
+		const handleName = handle(name);
+		throw redirect(303, `/${fam}/${encodeURIComponent(handleName)}`);
+	}
+};

frontend/src/routes/[fam]/join/+page.svelte

@@ -0,0 +1,65 @@
+<script lang="ts">
+	import { page } from '$app/state';
+	import { enhance } from '$app/forms';
+	import { Button } from '$lib/components';
+
+	const famSlug = page.params.fam;
+	let name = $state('');
+	let otp = $state(page.url.searchParams.get('code') || '');
+	let { form } = $props();
+</script>
+
+<svelte:head><title>Join {famSlug}</title></svelte:head>
+
+<main class="mx-auto flex min-h-screen max-w-md flex-col items-center justify-center px-6">
+	<section class="w-full rounded-2xl border border-slate-200 bg-white p-8 text-center shadow-sm">
+		<div class="mx-auto mb-4 flex h-12 w-12 items-center justify-center rounded-full bg-indigo-100 text-2xl">
+			🏠
+		</div>
+		<h1 class="text-xl font-bold text-slate-900">Join {famSlug}</h1>
+		<p class="mt-1 text-sm text-slate-500">
+			Enter your name and the code your parent gave you to get started.
+		</p>
+
+		<form
+			class="mt-6 flex flex-col gap-3"
+			method="POST"
+			use:enhance={() => {
+				return async ({ result, update }) => {
+					if (result.type === 'failure') {
+						name = (result.data as any)?.name || '';
+						otp = (result.data as any)?.otp || '';
+					}
+					await update();
+				};
+			}}
+		>
+			<input
+				type="text"
+				name="name"
+				bind:value={name}
+				placeholder="Your name"
+				autocomplete="name"
+				class="w-full rounded-lg border border-slate-300 px-4 py-3 text-center text-lg text-slate-900 outline-none focus:border-indigo-500 focus:ring-2 focus:ring-indigo-200"
+			/>
+			<input
+				type="text"
+				name="otp"
+				bind:value={otp}
+				inputmode="numeric"
+				maxlength="6"
+				placeholder="6-digit code"
+				autocomplete="one-time-code"
+				class="w-full rounded-lg border border-slate-300 px-4 py-3 text-center text-2xl tracking-[0.5em] text-slate-900 outline-none focus:border-indigo-500 focus:ring-2 focus:ring-indigo-200"
+			/>
+			{#if form?.error}
+				<p class="text-sm font-medium text-rose-600">{form.error}</p>
+			{/if}
+			<Button type="submit" variant="primary" size="lg">Join</Button>
+		</form>
+
+		<p class="mt-6 text-xs text-slate-400">
+			Code is valid for 20 minutes. Ask your parent for a new one if it expires.
+		</p>
+	</section>
+</main>

frontend/src/routes/[fam]/join/[username]/+page.svelte

@@ -22,7 +22,18 @@
 			gave you to get started.
 		</p>
 
-		<form class="mt-6 flex flex-col gap-3" method="POST" use:enhance={() => ({})}>
+		<form
+			class="mt-6 flex flex-col gap-3"
+			method="POST"
+			use:enhance={() => {
+				return async ({ result, update }) => {
+					if (result.type === 'failure') {
+						otp = (result.data as any)?.otp || '';
+					}
+					await update();
+				};
+			}}
+		>
 			<input
 				type="text"
 				name="otp"