refactor: make post header/nav cross-service (coop_url instead of url_for)

Blog overrides these with its own url_for + HTMX versions.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

suma_browser/templates/_types/post/_nav.html

@@ -6,11 +6,3 @@
         {% include '_types/post/admin/_nav_entries.html' %}
       </div>
     {% endif %}
-
-    {# Admin link #}
-  {% if post and has_access('blog.post.admin.admin') %}
-      {% import 'macros/links.html' as links %}
-      {% call links.link(url_for('blog.post.admin.admin', slug=post.slug), hx_select_search, select_colours, True, aclass=styles.nav_button) %}
-        <i class="fa fa-cog" aria-hidden="true"></i>
-      {% endcall %}
-  {% endif %}

suma_browser/templates/_types/post/header/_header.html

@@ -1,7 +1,7 @@
 {% import 'macros/links.html' as links %}
 {% macro header_row(oob=False) %}
   {% call links.menu_row(id='post-row', oob=oob) %}
-    {% call links.link(url_for('blog.post.post_detail', slug=post.slug), hx_select_search ) %}
+    <a href="{{ coop_url('/' + post.slug + '/') }}" class="flex items-center gap-2 px-3 py-2 rounded whitespace-normal text-center break-words leading-snug">
       {% if post.feature_image %}
       <img
           src="{{ post.feature_image }}"
@@ -11,7 +11,7 @@
       <span>
         {{ post.title | truncate(160, True, '…') }}
       </span>
-    {% endcall %}
+    </a>
     {% call links.desktop_nav() %}
       {% include '_types/post/_nav.html' %}
     {% endcall %}