fix(theme): dark-theme login box, feedback messages, and nav logout link

- Override the Login plugin's white #grav-login box to use dark theme tokens
- Style flash/form notices (.notices, #messages .toast) globally on-theme;
  override markdown-notices' bright per-colour variant backgrounds so error/
  success/warning messages stay dark with a coloured left border
- Add a Logout link to the main nav (authenticated-only, plain nav style);
  no login link in the menu

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Rw9Tceo6DSzVqWKkjVJpHZ

themes/intotheeast/templates/partials/base.html.twig

@@ -30,6 +30,7 @@
             {% if grav.user.authenticated %}
             <a href="{{ base_url_absolute }}/post"{% if page.template == 'post-form' %} aria-current="page"{% endif %}>New Post</a>
             <a href="{{ base_url_absolute }}/gpx-manager"{% if page.template == 'gpx-manager' %} aria-current="page"{% endif %}>GPX Manager</a>
+            <a href="{{ url(uri.addNonce((uri.path)|trim('/') ~ '/task' ~ config.system.param_sep ~ 'login.logout', 'logout-form', 'logout-nonce'))|e }}">Logout</a>
             {% endif %}
         </nav>
         {% endblock %}