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/_nav.html

@@ -1,53 +1,43 @@
 <nav class="nav">
-  <!--
-        admin_dashboard.html
-        admin_newsletter.html
-        admin_newsletter_create.html
-        admin_settings.html
-        admin_submissions.html
-        admin_embeds.html
-
-        newsletter_manage.html
-        unsubscribe_confirmation.html
-        -->
   <a
-    href="/admin/"
-    style="color: #007bff; text-decoration: none; margin-right: 20px"
+    href="{{ url_for('admin.dashboard') }}"
+    class="nav-link{% if request.path in ['/admin', '/admin/'] %} active{% endif %}"
     >Dashboard</a
   >
   <a
-    href="/admin/submissions"
-    style="color: #007bff; text-decoration: none; margin-right: 20px"
+    href="{{ url_for('admin.submissions') }}"
+    class="nav-link{% if request.path.startswith('/admin/submissions') %} active{% endif %}"
     >Contact Submissions</a
   >
   <a
-    href="/admin/newsletter"
-    style="color: #007bff; text-decoration: none; margin-right: 20px"
+    href="{{ url_for('admin.newsletter_subscribers') }}"
+    class="nav-link{% if request.path == '/admin/newsletter' %} active{% endif %}"
     >Subscribers</a
   >
   <a
-    href="/admin/newsletter/create"
-    style="color: #007bff; text-decoration: none; margin-right: 20px"
+    href="{{ url_for('admin.newsletter_create') }}"
+    class="nav-link{% if request.path.startswith('/admin/newsletter/create') %} active{% endif %}"
     >Create Newsletter</a
   >
   <a
-    href="/admin/embeds"
-    style="color: #007bff; text-decoration: none; margin-right: 20px"
+    href="{{ url_for('admin.embeds') }}"
+    class="nav-link{% if request.path.startswith('/admin/embeds') %} active{% endif %}"
     >Embeds</a
   >
   <a
-    href="/admin/email-templates"
-    style="color: #007bff; text-decoration: none; margin-right: 20px"
+    href="{{ url_for('admin.email_settings_page') }}"
+    class="nav-link{% if request.path.startswith('/admin/email-settings') %} active{% endif %}"
+    >Email Settings</a
+  >
+  <a
+    href="{{ url_for('admin.email_templates') }}"
+    class="nav-link{% if request.path.startswith('/admin/email-templates') %} active{% endif %}"
     >Email Templates</a
   >
   <a
-    href="/admin/settings"
-    style="color: #007bff; text-decoration: none; margin-right: 20px"
+    href="{{ url_for('admin.settings_page') }}"
+    class="nav-link{% if request.path.startswith('/admin/settings') and not request.path.startswith('/admin/email-settings') %} active{% endif %}"
     >Settings</a
   >
-  <a
-    href="{{ url_for('auth.logout') }}"
-    style="color: #007bff; text-decoration: none"
-    >Logout</a
-  >
+  <a href="{{ url_for('auth.logout') }}" class="nav-link">Logout</a>
 </nav>