Add per-app AP social UI for blog, market, and events

Lightweight social pages (search, follow/unfollow, followers, following,
actor timeline) auto-registered for AP-enabled apps via shared blueprint.
Federation keeps the full social hub. Followers scoped per app_domain;
post cards show "View on Hub" link instead of interaction buttons.

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

shared/browser/templates/social/_timeline_items.html

@@ -0,0 +1,13 @@
+{% for item in items %}
+  {% include "social/_post_card.html" %}
+{% endfor %}
+
+{% if items %}
+  {% set last = items[-1] %}
+  {% if timeline_type == "actor" %}
+    <div hx-get="{{ url_for('ap_social.actor_timeline_page', id=actor_id, before=last.published.isoformat()) }}"
+         hx-trigger="revealed"
+         hx-swap="outerHTML">
+    </div>
+  {% endif %}
+{% endif %}