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/lib/auth/server.ts

@@ -3,6 +3,8 @@ import { genericOAuth } from "better-auth/plugins";
 import { drizzleAdapter } from "better-auth/adapters/drizzle";
 import { db, users, sessions, accounts, verifications, eq, count } from "@epicure/db";
 import { sendEmail, verifyEmailHtml, resetPasswordHtml, welcomeHtml } from "@/lib/email";
+import { isSignupsDisabled } from "@/lib/site-settings";
+import { findValidInvite, consumeInvite, INVITE_COOKIE } from "@/lib/invites";
 
 export const auth = betterAuth({
   trustedOrigins: [process.env["BETTER_AUTH_URL"] ?? "http://localhost:3000"],
@@ -82,12 +84,28 @@ export const auth = betterAuth({
   databaseHooks: {
     user: {
       create: {
-        after: async (user) => {
+        before: async (user, context) => {
+          if (!(await isSignupsDisabled())) return;
+
+          const token = context?.getCookie(INVITE_COOKIE);
+          const invite = token ? await findValidInvite(token, user.email) : null;
+          if (!invite) return false;
+
+          return { data: { ...user, role: invite.role, tier: invite.tier } };
+        },
+        after: async (user, context) => {
           // First registered user becomes admin
           const result = await db.select({ total: count() }).from(users);
           if ((result[0]?.total ?? 0) === 1) {
             await db.update(users).set({ role: "admin" }).where(eq(users.id, user.id));
           }
+
+          // Consume the invite that gated this signup, if any (regardless of
+          // whether signups have since been re-enabled/disabled).
+          const token = context?.getCookie(INVITE_COOKIE);
+          const invite = token ? await findValidInvite(token, user.email) : null;
+          if (invite) await consumeInvite(invite.id, user.id);
+
           // Welcome email (fire and forget)
           sendEmail({
             to: user.email,