feat(auth): add TOTP 2FA setup and login verification

- add user twofa fields and migration

- add 2FA setup/enable/disable endpoints

- enforce OTP on login when 2FA enabled

- add web login OTP field and settings UI

web/src/chat/types.ts

@@ -77,6 +77,7 @@ export interface AuthUser {
   bio?: string | null;
   avatar_url: string | null;
   email_verified: boolean;
+  twofa_enabled?: boolean;
   allow_private_messages: boolean;
   created_at: string;
   updated_at: string;