Add TOTP-based two-factor authentication

- Add 2FA setup, enable, disable, and backup code management
- Integrate 2FA challenge flow into login process
- Add frontend modal for 2FA configuration
- Support backup codes for account recovery

frontend/src/api/backend/getToken.ts

@@ -1,9 +1,22 @@
 import * as api from "./base";
-import type { TokenResponse } from "./responseTypes";
+import type { TokenResponse, TwoFactorChallengeResponse } from "./responseTypes";
 
-export async function getToken(identity: string, secret: string): Promise<TokenResponse> {
+export type LoginResponse = TokenResponse | TwoFactorChallengeResponse;
+
+export function isTwoFactorChallenge(response: LoginResponse): response is TwoFactorChallengeResponse {
+	return "requires2fa" in response && response.requires2fa === true;
+}
+
+export async function getToken(identity: string, secret: string): Promise<LoginResponse> {
 	return await api.post({
 		url: "/tokens",
 		data: { identity, secret },
 	});
 }
+
+export async function verify2FA(challengeToken: string, code: string): Promise<TokenResponse> {
+	return await api.post({
+		url: "/tokens/2fa",
+		data: { challengeToken, code },
+	});
+}