feat: signup toggle, invite links, admin-created users

- New invites table: token-gated signup, optional email lock,
  role/tier override, single-use, expiry.
- SIGNUPS_DISABLED site setting toggle at /admin/settings.
- databaseHooks.user.create gate in auth/server.ts blocks new account
  creation (email + Google OAuth) when disabled unless a valid invite
  cookie is present; applies invite role/tier and marks it consumed.
- /admin/invites: create/list/revoke shareable invite links.
- /admin/users: "Create user" dialog — admin sets email/role/tier,
  account is pre-verified, user gets a set-password email (admin
  never sees a password).
- Signup page reads ?invite=, validates via public
  /api/v1/invites/[token], locks the form when signups are closed
  and no valid invite is present.
- proxy.ts: allowlist /api/v1/invites/ for anonymous invite checks.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/web/app/admin/users/page.tsx

@@ -4,6 +4,7 @@ import { users } from "@epicure/db";
 import { desc } from "@epicure/db";
 import { Badge } from "@/components/ui/badge";
 import { Avatar, AvatarFallback, AvatarImage } from "@/components/ui/avatar";
+import { CreateUserDialog } from "@/components/admin/create-user-dialog";
 import Link from "next/link";
 
 export const metadata: Metadata = { title: "User Management" };
@@ -28,7 +29,10 @@ export default async function AdminUsersPage() {
 
   return (
     <div className="space-y-6">
-      <h1 className="text-2xl font-bold tracking-tight">Users</h1>
+      <div className="flex items-center justify-between">
+        <h1 className="text-2xl font-bold tracking-tight">Users</h1>
+        <CreateUserDialog />
+      </div>
       <div className="rounded-md border">
         <table className="w-full text-sm">
           <thead className="border-b bg-muted/50">