Incorporate art-dag-mono repo into artdag/ subfolder

Merges full history from art-dag/mono.git into the monorepo
under the artdag/ directory. Contains: core (DAG engine),
l1 (Celery rendering server), l2 (ActivityPub registry),
common (shared templates/middleware), client (CLI), test (e2e).

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

git-subtree-dir: artdag
git-subtree-mainline: 1a179de547
git-subtree-split: 4c2e716558

artdag/l2/app/templates/activities/list.html

@@ -0,0 +1,39 @@
+{% extends "base.html" %}
+
+{% block title %}Activities - Art-DAG{% endblock %}
+
+{% block content %}
+<div class="max-w-4xl mx-auto">
+    <div class="flex items-center justify-between mb-6">
+        <h1 class="text-2xl font-bold">Activities</h1>
+    </div>
+
+    {% if activities %}
+    <div class="space-y-4">
+        {% for activity in activities %}
+        <a href="/activities/{{ activity.activity_id }}"
+           class="block bg-gray-800 border border-gray-700 rounded-lg p-4 hover:border-blue-500 transition-colors">
+            <div class="flex items-center justify-between mb-2">
+                <span class="text-blue-400 font-medium">{{ activity.activity_type }}</span>
+                <span class="text-gray-500 text-sm">{{ activity.published }}</span>
+            </div>
+            <div class="text-gray-300 text-sm truncate">
+                {{ activity.actor_id }}
+            </div>
+        </a>
+        {% endfor %}
+    </div>
+
+    {% if has_more %}
+    <div class="mt-6 text-center">
+        <a href="?offset={{ offset + limit }}&limit={{ limit }}"
+           class="text-blue-400 hover:text-blue-300">Load More</a>
+    </div>
+    {% endif %}
+    {% else %}
+    <div class="text-center py-12 text-gray-400">
+        <p>No activities yet.</p>
+    </div>
+    {% endif %}
+</div>
+{% endblock %}