fix(mnemonic): ensure account is initialized when signing transactions

This fixes the bug where signing transactions with the mnemonic wallet fails under certain
circumstances because the account is not initialized despite being in a valid connection session.

packages/use-wallet/src/wallets/mnemonic.ts

@@ -226,6 +226,8 @@ export class MnemonicWallet extends BaseWallet {
       this.logger.debug('Signing transactions...', { txnGroup, indexesToSign })
       let txnsToSign: algosdk.Transaction[] = []
 
+      const account = this.account || this.initializeAccount()
+
       // Determine type and process transactions for signing
       if (isTransactionArray(txnGroup)) {
         const flatTxns: algosdk.Transaction[] = flattenTxnGroup(txnGroup)
@@ -236,7 +238,7 @@ export class MnemonicWallet extends BaseWallet {
       }
 
       // Sign transactions
-      const signedTxns = txnsToSign.map((txn) => txn.signTxn(this.account!.sk))
+      const signedTxns = txnsToSign.map((txn) => txn.signTxn(account.sk))
       this.logger.debug('Transactions signed successfully', { signedTxns })
       return signedTxns
     } catch (error: any) {