Add referral program invitation and voucher email templates

- Created `referralprogram-invitation.html.twig` for sending invitations to friends to join the referral program.
- Created `referralprogram-voucher.html.twig` for notifying users about their voucher after referring a friend.
- Both templates include responsive design and utilize the modern email layout.
- Added translation support for various text elements within the templates.

mails/themes/classic/core/cheque.html.twig

@@ -0,0 +1,92 @@
+{% extends '@MailThemes/classic/components/layout.html.twig' %}
+
+{% block content %}
+<tr>
+  <td align="center" class="titleblock">
+    <font size="2" face="{{ languageDefaultFont }}Open-sans, sans-serif" color="#555454">
+      <span class="title">{{ 'Hi {firstname} {lastname},'|trans({}, 'Emails.Body', locale) }}</span><br/>
+      <span class="subtitle">{{ 'Thank you for shopping with {shop_name}!'|trans({}, 'Emails.Body', locale) }}</span>
+    </font>
+  </td>
+</tr>
+<tr>
+  <td class="space_footer">&nbsp;</td>
+</tr>
+<tr>
+  <td class="box" style="border:1px solid #D6D4D4;">
+    <table class="table">
+      <tr>
+        <td width="10">&nbsp;</td>
+        <td>
+          <font size="2" face="{{ languageDefaultFont }}Open-sans, sans-serif" color="#555454">
+            {% if templateType == 'html' %}
+
+              <p style="border-bottom:1px solid #D6D4D4;">
+                {{ 'Order {order_name}'|trans({}, 'Emails.Body', locale) }}&nbsp;-&nbsp;{{ 'Awaiting check payment'|trans({}, 'Emails.Body', locale)|raw }}
+              </p>
+
+{% endif %}
+            <span>
+              {{ 'Your order with the reference [1]{order_name}[/1] has been placed successfully and will be [1]shipped as soon as we receive your payment[/1].'|trans({'[1]': '<span><strong>', '[/1]': '</strong></span>'}, 'Emails.Body', locale)|raw }}
+            </span>
+          </font>
+        </td>
+        <td width="10">&nbsp;</td>
+      </tr>
+    </table>
+  </td>
+</tr>
+<tr>
+  <td class="space_footer">&nbsp;</td>
+</tr>
+<tr>
+  <td class="box" style="border:1px solid #D6D4D4;">
+    <table class="table">
+      <tr>
+        <td width="10">&nbsp;</td>
+        <td>
+          <font size="2" face="{{ languageDefaultFont }}Open-sans, sans-serif" color="#555454">
+            <p style="border-bottom:1px solid #D6D4D4;">
+              {{ 'You have selected to pay by check.'|trans({}, 'Emails.Body', locale)|raw }}
+            </p>
+            <span>
+              {{ 'Here are the bank details for your check:'|trans({}, 'Emails.Body', locale)|raw }}<br/>
+              <span><strong>{{ 'Amount:'|trans({}, 'Emails.Body', locale)|raw }}</strong></span> {total_paid}<br/>
+              <span><strong>{{ 'Payable to the order of:'|trans({}, 'Emails.Body', locale)|raw }}</strong></span> {check_name}<br/>
+              <span><strong>{{ 'Please mail your check to:'|trans({}, 'Emails.Body', locale)|raw }}</strong></span>
+              {% if templateType == 'html' %}
+{check_address_html}
+{% endif %}
+              {% if templateType == 'txt' %}
+{check_address}
+{% endif %}
+            </span>
+          </font>
+        </td>
+        <td width="10">&nbsp;</td>
+      </tr>
+    </table>
+  </td>
+</tr>
+<tr>
+  <td class="space_footer">&nbsp;</td>
+</tr>
+<tr>
+  <td class="linkbelow">
+    <font size="2" face="{{ languageDefaultFont }}Open-sans, sans-serif" color="#555454">
+      <span>
+        {{ 'Follow your order and download your invoice on our shop, go to the <a href="{history_url}" target="_blank">%order_history_label%</a> section of your customer account.'|trans({'%order_history_label%': 'Order history and details'|trans({}, 'Shop.Theme.Customeraccount', locale)}, 'Emails.Body', locale)|raw }}
+      </span>
+    </font>
+  </td>
+</tr>
+<tr>
+  <td class="linkbelow">
+    <font size="2" face="{{ languageDefaultFont }}Open-sans, sans-serif" color="#555454">
+      <span>
+        {{ 'If you have a guest account, you can follow your order via the <a href="{guest_tracking_url}" target="_blank">%guest_tracking_label%</a> section on our shop.'|trans({'%guest_tracking_label%': 'Guest Tracking'|trans({}, 'Shop.Theme.Customeraccount', locale)}, 'Emails.Body', locale)|raw }}
+      </span>
+    </font>
+  </td>
+</tr>
+{% endblock %}