feat: Add email settings management and templates functionality

- Implemented email settings configuration in the admin panel, allowing for SMTP settings and notification preferences.
- Created a new template for email settings with fields for SMTP host, port, username, password, sender address, and recipients.
- Added JavaScript functionality to handle loading, saving, and validating email settings.
- Introduced email templates management, enabling the listing, editing, and saving of email templates.
- Updated navigation to include links to email settings and templates.
- Added tests for email settings and templates to ensure proper functionality and validation.

templates/admin/admin_email_templates.html

@@ -1,20 +1,41 @@
 {% extends "_base.html" %} {% block title %}Email Templates{% endblock %} {%
 block heading %}Email Templates{% endblock %} {% block extra_styles %}
-<link rel="stylesheet" href="/static/css/admin.css" /> {% endblock %} {% block
-content %}
-<div class="settings-management">
-  <h2>Newsletter Confirmation Template</h2>
-  <p>Edit the HTML template used for the newsletter confirmation email.</p>
-  <div id="message"></div>
-  <form id="templateForm">
-    <div class="form-group">
-      <label for="newsletterTemplate">Template HTML</label>
-      <textarea id="newsletterTemplate" rows="15" cols="80"></textarea>
-    </div>
-    <div class="form-group">
-      <button class="btn btn-primary" type="submit">Save Template</button>
-    </div>
-  </form>
+<link rel="stylesheet" href="/static/css/admin.css" />
+{% endblock %} {% block content %}
+<div class="email-templates-container" id="emailTemplatesPage">
+  <aside
+    class="email-templates-list"
+    id="emailTemplatesList"
+    aria-label="Available email templates"
+  ></aside>
+
+  <section class="email-template-editor">
+    <div id="templateMessage" class="message" style="display: none"></div>
+    <h2 id="templateTitle">Select a template to start editing</h2>
+    <p id="templateDescription" class="template-description"></p>
+
+    <form id="emailTemplateForm">
+      <div class="form-group">
+        <label for="templateContent">Template HTML</label>
+        <textarea
+          id="templateContent"
+          rows="20"
+          class="template-content"
+          disabled
+        ></textarea>
+      </div>
+      <div class="form-actions">
+        <button
+          class="btn btn-primary"
+          type="submit"
+          id="saveTemplateButton"
+          disabled
+        >
+          Save Template
+        </button>
+      </div>
+    </form>
+  </section>
 </div>
 {% endblock %} {% block extra_scripts %}
 <script src="/static/js/admin.js"></script>