feat: two-factor authentication (TOTP + backup codes)

Uses better-auth's built-in twoFactor plugin rather than hand-rolling
TOTP — adds the two_factors table and users.twoFactorEnabled, wires
the server/client plugins (allowPasswordless: true so OAuth-only
accounts aren't locked out of managing 2FA), and adds a custom rate
limit for the verify endpoints (5/min — far stricter than the default
100/10s, since a 6-digit code has a much smaller keyspace than a
password).

New Settings → Security section walks through enable (password
confirm -> QR + backup codes -> confirm a live code before it's
actually turned on, per the plugin's default flow) and disable. New
/verify-2fa page handles the post-password mid-login step, with a
backup-code fallback. Verified live end-to-end: enable, confirm,
forced re-auth on next sign-in, TOTP accepted, backup code accepted
(single-use), disable.

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

apps/web/app/(app)/settings/security/page.tsx

@@ -1,6 +1,7 @@
 import type { Metadata } from "next";
 import { headers } from "next/headers";
 import { auth } from "@/lib/auth/server";
+import { db, accounts, users, eq, and } from "@epicure/db";
 import { SecurityForm } from "@/components/settings/security-form";
 
 export const metadata: Metadata = {};
@@ -9,5 +10,16 @@ export default async function SecurityPage() {
   const session = await auth.api.getSession({ headers: await headers() });
   if (!session) return null;
 
-  return <SecurityForm currentEmail={session.user.email} />;
+  const [dbUser, credentialAccount] = await Promise.all([
+    db.query.users.findFirst({ where: eq(users.id, session.user.id), columns: { twoFactorEnabled: true } }),
+    db.query.accounts.findFirst({ where: and(eq(accounts.userId, session.user.id), eq(accounts.providerId, "credential")) }),
+  ]);
+
+  return (
+    <SecurityForm
+      currentEmail={session.user.email}
+      twoFactorEnabled={dbUser?.twoFactorEnabled ?? false}
+      hasPassword={!!credentialAccount}
+    />
+  );
 }