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/routers/__init__.py

@@ -0,0 +1,25 @@
+"""
+L2 Server Routers.
+
+Each router handles a specific domain of functionality.
+"""
+
+from . import auth
+from . import assets
+from . import activities
+from . import anchors
+from . import storage
+from . import users
+from . import renderers
+from . import federation
+
+__all__ = [
+    "auth",
+    "assets",
+    "activities",
+    "anchors",
+    "storage",
+    "users",
+    "renderers",
+    "federation",
+]