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/core/artdag/__init__.py

@@ -0,0 +1,61 @@
+# artdag - Content-addressed DAG execution engine with ActivityPub ownership
+#
+# A standalone execution engine that processes directed acyclic graphs (DAGs)
+# where each node represents an operation. Nodes are content-addressed for
+# automatic caching and deduplication.
+#
+# Core concepts:
+# - Node: An operation with type, config, and inputs
+# - DAG: A graph of nodes with a designated output node
+# - Executor: Implements the actual operation for a node type
+# - Engine: Executes DAGs by resolving dependencies and running executors
+
+from .dag import Node, DAG, DAGBuilder, NodeType
+from .cache import Cache, CacheEntry
+from .executor import Executor, register_executor, get_executor
+from .engine import Engine
+from .registry import Registry, Asset
+from .activities import Activity, ActivityStore, ActivityManager, make_is_shared_fn
+
+# Analysis and planning modules (optional, require extra dependencies)
+try:
+    from .analysis import Analyzer, AnalysisResult
+except ImportError:
+    Analyzer = None
+    AnalysisResult = None
+
+try:
+    from .planning import RecipePlanner, ExecutionPlan, ExecutionStep
+except ImportError:
+    RecipePlanner = None
+    ExecutionPlan = None
+    ExecutionStep = None
+
+__all__ = [
+    # Core
+    "Node",
+    "DAG",
+    "DAGBuilder",
+    "NodeType",
+    "Cache",
+    "CacheEntry",
+    "Executor",
+    "register_executor",
+    "get_executor",
+    "Engine",
+    "Registry",
+    "Asset",
+    "Activity",
+    "ActivityStore",
+    "ActivityManager",
+    "make_is_shared_fn",
+    # Analysis (optional)
+    "Analyzer",
+    "AnalysisResult",
+    # Planning (optional)
+    "RecipePlanner",
+    "ExecutionPlan",
+    "ExecutionStep",
+]
+
+__version__ = "0.1.0"