Enhance UI and functionality for admin dashboard and user management

- Update `_base_context` to include `active_nav` for dynamic navigation highlighting.
- Revamp `base.html` to improve header layout and navigation links for better user experience.
- Redesign `dashboard.html` to include statistics for new and edited articles, enhancing visibility of content changes.
- Improve `users.html` layout for user management, adding detailed user roles and status indicators.
- Update CSS styles for a cohesive design across the application, introducing new color variables and layout adjustments.

app/templates/login.html

@@ -1,19 +1,22 @@
 {% extends "base.html" %}
+{% block title %}Anmelden{% endblock %}
+{% block body_class %}login-page{% endblock %}
 {% block content %}
-<section class="card narrow">
-    <h2>Login</h2>
+<section class="card login-card">
+    <h2>Anmelden</h2>
+    <p class="login-subtitle">Thomas-Krenn Wiki Newsletter Admin</p>
     {% 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
-            <input type="email" name="email" required>
+            <input type="email" name="email" required autocomplete="username" placeholder="name@firma.de">
         </label>
         <label>Passwort
-            <input type="password" name="password" required>
+            <input type="password" name="password" required autocomplete="current-password">
         </label>
-        <button type="submit">Anmelden</button>
+        <button type="submit" class="btn-primary btn-block">Anmelden</button>
     </form>
 </section>
 {% endblock %}