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/test/sexp_effects/__init__.py

@@ -0,0 +1,32 @@
+"""
+S-Expression Effects System
+
+Safe, shareable effects defined in S-expressions.
+"""
+
+from .parser import parse, parse_file, Symbol, Keyword
+from .interpreter import (
+    Interpreter,
+    get_interpreter,
+    load_effect,
+    load_effects_dir,
+    run_effect,
+    list_effects,
+    make_process_frame,
+)
+from .primitives import PRIMITIVES
+
+__all__ = [
+    'parse',
+    'parse_file',
+    'Symbol',
+    'Keyword',
+    'Interpreter',
+    'get_interpreter',
+    'load_effect',
+    'load_effects_dir',
+    'run_effect',
+    'list_effects',
+    'make_process_frame',
+    'PRIMITIVES',
+]