Team invitation flow is clearly presented

A buried or broken invitation flow directly limits expansion revenue in any multi-user SaaS. If an invited user clicks an email link and sees a 'User not found' error instead of a signup prompt, that seat is lost — and the inviter loses confidence in the product. CWE-284 (improper access control) applies when the invite acceptance route fails to redirect non-users to registration, effectively creating a dead end that prevents legitimate account creation through a valid access path.

In the invite acceptance handler at src/app/invite/[token]/page.tsx, redirect non-users to signup with the invite context preserved:

const invite = await getInviteByToken(token);
if (!invite || invite.expiresAt < new Date()) notFound();

const user = await getUserByEmail(invite.email);
if (!user) {
  redirect(`/signup?email=${encodeURIComponent(invite.email)}&invite=${token}`);
}

await acceptInvite(invite.id, user.id);
redirect('/dashboard');

Also add an 'Invite teammates' entry to src/components/Sidebar.tsx reachable within 2 clicks of the dashboard — users shouldn't have to dig through settings to find it.