Remove unused templates for newsletter creation, settings, and submissions; update unsubscribe confirmation link; add tests for email templates API.

templates/_nav.html

@@ -0,0 +1,53 @@
+<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"
+    >Dashboard</a
+  >
+  <a
+    href="/admin/submissions"
+    style="color: #007bff; text-decoration: none; margin-right: 20px"
+    >Contact Submissions</a
+  >
+  <a
+    href="/admin/newsletter"
+    style="color: #007bff; text-decoration: none; margin-right: 20px"
+    >Subscribers</a
+  >
+  <a
+    href="/admin/newsletter/create"
+    style="color: #007bff; text-decoration: none; margin-right: 20px"
+    >Create Newsletter</a
+  >
+  <a
+    href="/admin/embeds"
+    style="color: #007bff; text-decoration: none; margin-right: 20px"
+    >Embeds</a
+  >
+  <a
+    href="/admin/email-templates"
+    style="color: #007bff; text-decoration: none; margin-right: 20px"
+    >Email Templates</a
+  >
+  <a
+    href="/admin/settings"
+    style="color: #007bff; text-decoration: none; margin-right: 20px"
+    >Settings</a
+  >
+  <a
+    href="{{ url_for('auth.logout') }}"
+    style="color: #007bff; text-decoration: none"
+    >Logout</a
+  >
+</nav>