Update configuration and enhance newsletter generation features

- Change WIKI_API_URL in .env.example and config to point to the new API endpoint.
- Set COOKIE_SECURE to false for local development in .env.example and config.
- Improve the newsletter generation logic to handle new and edited articles separately.
- Add display options for showing date, user, and category in the newsletter output.
- Enhance error handling for Wiki API requests and update templates for better user feedback.
- Update CSS for new UI elements and improve overall layout in dashboard and login pages.

app/templates/login.html

@@ -2,6 +2,9 @@
 {% block content %}
 <section class="card narrow">
     <h2>Login</h2>
+    {% if error_message %}
+    <p class="error">{{ error_message }}</p>
+    {% endif %}
     <form method="post" action="/login" class="form-grid">
         <input type="hidden" name="csrf_token" value="{{ csrf_token }}">
         <label>E-Mail