feat(nav): add New Post + GPX Manager links for logged-in users

Both links render only when grav.user.authenticated; anonymous nav
(Home, Past Trips) is unchanged. Active-page highlight via aria-current.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Mpdu3Dt1iVoozHwAMyjrbn

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

@@ -27,6 +27,10 @@
         <nav class="site-nav" id="site-nav" aria-label="Main navigation">
             <a href="{{ base_url_absolute }}"{% if page.template == 'home' %} aria-current="page"{% endif %}>Home</a>
             <a href="{{ base_url_absolute }}/trips"{% if page.template == 'trips' %} aria-current="page"{% endif %}>Past Trips</a>
+            {% 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>
+            {% endif %}
         </nav>
         {% endblock %}
     </header>