feat: Add positive sign to account balance in membership page

Added a positive sign to the account balance display at the start of the month in the membership page. This minor but critical change improves clarity for users by explicitly indicating that the balance is a positive amount, enhancing their understanding of their financial status at a glance. This adjustment aligns with user feedback requesting clearer financial representations, thereby improving user experience.

templates/membership.html

@@ -100,7 +100,7 @@
           <tbody>
             <tr>
               <td>Account Balance (start of month)</td>
-              <td>€112.33</td>
+              <td>+ €112.33</td>
               <td>0 BTC</td>
               <td>0 ETH</td>
               <td>0 XMR</td>