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/api/v1/admin/invites/route.ts

@@ -0,0 +1,57 @@
+import { NextRequest, NextResponse } from "next/server";
+import { requireAdmin } from "@/lib/api-auth";
+import { db, auditLogs } from "@epicure/db";
+import { createInvite, listInvites } from "@/lib/invites";
+import { randomUUID } from "crypto";
+
+const VALID_ROLES = ["user", "moderator", "admin"] as const;
+const VALID_TIERS = ["free", "pro"] as const;
+
+export async function GET() {
+  const { response } = await requireAdmin();
+  if (response) return response;
+
+  const invites = await listInvites();
+  return NextResponse.json({ invites });
+}
+
+export async function POST(req: NextRequest) {
+  const { session, response } = await requireAdmin();
+  if (response) return response;
+
+  const body = (await req.json()) as {
+    email?: string;
+    role?: string;
+    tier?: string;
+    expiresInDays?: number;
+  };
+
+  const role = body.role ?? "user";
+  const tier = body.tier ?? "free";
+  if (!VALID_ROLES.includes(role as (typeof VALID_ROLES)[number])) {
+    return NextResponse.json({ error: "Invalid role" }, { status: 400 });
+  }
+  if (!VALID_TIERS.includes(tier as (typeof VALID_TIERS)[number])) {
+    return NextResponse.json({ error: "Invalid tier" }, { status: 400 });
+  }
+
+  const invite = await createInvite({
+    createdById: session!.user.id,
+    email: body.email,
+    role: role as (typeof VALID_ROLES)[number],
+    tier: tier as (typeof VALID_TIERS)[number],
+    expiresInDays: body.expiresInDays ?? 7,
+  });
+
+  await db.insert(auditLogs).values({
+    id: randomUUID(),
+    userId: session!.user.id,
+    action: "admin.invite.create",
+    targetType: "invite",
+    targetId: invite!.id,
+    metadata: JSON.stringify({ email: body.email, role, tier }),
+    createdAt: new Date(),
+  });
+
+  return NextResponse.json({ invite });
+}