Add OxaPay Wallet to Wallets Page

OxaPay Wallet is a centralized multi-currency wallet integrated within the OxaPay platform, supporting Bitcoin Cash and various cryptocurrencies. The wallet is also available in Telegram and browser extension versions, providing seamless payments, instant swaps without blockchain fees, and secure global transactions.  
This commit adds the OxaPay Wallet logo and official link (https://oxapay.com/wallet) to the wallets section.

Author: kevin-san0

views/index.html.erb

@@ -241,6 +241,9 @@
           <div class="col-sm-6 col-md-3 vertical-align">
             <a href="https://edgesecure.co/" target="_blank"><img loading="lazy" alt="Edge" src="/img/wallets/edge.webp"></a>
           </div>
+          <div class="col-sm-6 col-md-3 vertical-align">
+            <a href="https://oxapay.com" target="_blank"><img loading="lazy" alt="OxaPay Wallet" src="/img/wallets/oxapay_wallet.webp"></a>
+          </div>
           <div class="col-sm-6 col-md-3 vertical-align">
             <a href="https://stackwallet.com/" target="_blank"><img loading="lazy" alt="Stack Wallet" src="/img/wallets/stack.webp"></a>
           </div>