feat: send L1 server URL when publishing to L2

- Include l1_server in record-run request
- Enables many-to-many L1/L2 topology

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

artdag.py

@@ -411,11 +411,11 @@ def publish(run_id, output_name):
         click.echo("Not logged in. Please run: artdag login <username>", err=True)
         sys.exit(1)
 
-    # Post to L2 server with auth
+    # Post to L2 server with auth, including which L1 server has the run
     try:
         resp = requests.post(
             f"{get_l2_server()}/registry/record-run",
-            json={"run_id": run_id, "output_name": output_name},
+            json={"run_id": run_id, "output_name": output_name, "l1_server": get_server()},
             headers={"Authorization": f"Bearer {token_data['access_token']}"}
         )
         if resp.status_code == 401: