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/server.py

@@ -0,0 +1,26 @@
+#!/usr/bin/env python3
+"""
+Art DAG L2 Server - ActivityPub
+
+Minimal entry point that uses the modular app factory.
+All routes are defined in app/routers/.
+All templates are in app/templates/.
+"""
+
+import logging
+import os
+
+# Configure logging
+logging.basicConfig(
+    level=logging.INFO,
+    format='%(asctime)s %(levelname)s %(name)s: %(message)s'
+)
+
+# Import the app from the factory
+from app import app
+
+if __name__ == "__main__":
+    import uvicorn
+    host = os.environ.get("HOST", "0.0.0.0")
+    port = int(os.environ.get("PORT", "8200"))
+    uvicorn.run("server:app", host=host, port=port, workers=4)