Fix launch crash: lazy-load amazon-cognito-identity-js

The library's module graph eagerly initializes native module bindings
(RNAWSCognito) during import, causing a TypeError on startup since the
native pod isn't linked. Dynamic import defers loading until the user
actually taps "Sign In" with credentials, keeping it off the critical
startup path entirely.

mobile/src/lib/api/cognito-auth.ts

@@ -1,16 +1,6 @@
-import {
+import type { CognitoUserSession } from 'amazon-cognito-identity-js';
-  CognitoUserPool,
-  CognitoUser,
-  AuthenticationDetails,
-  CognitoUserSession,
-} from 'amazon-cognito-identity-js';
 import Config from '../../config';
 
-const userPool = new CognitoUserPool({
-  UserPoolId: Config.COGNITO_USER_POOL_ID,
-  ClientId: Config.COGNITO_CLIENT_ID,
-});
-
 export interface CognitoTokens {
   accessToken: string;
   idToken: string;
@@ -28,10 +18,22 @@ function extractTokens(session: CognitoUserSession): CognitoTokens {
   };
 }
 
-export function authenticateWithCredentials(
+export async function authenticateWithCredentials(
   email: string,
   password: string,
 ): Promise<CognitoTokens> {
+  // Lazy-load to keep amazon-cognito-identity-js out of the startup module graph
+  const {
+    CognitoUserPool,
+    CognitoUser,
+    AuthenticationDetails,
+  } = await import('amazon-cognito-identity-js');
+
+  const userPool = new CognitoUserPool({
+    UserPoolId: Config.COGNITO_USER_POOL_ID,
+    ClientId: Config.COGNITO_CLIENT_ID,
+  });
+
   return new Promise((resolve, reject) => {
     const cognitoUser = new CognitoUser({
       Username: email,