feat: Add complete Python workflow executor from AutoMetabuilder

Add full Python workflow execution engine with:

Core Executor:
- engine.py: WorkflowEngine for running n8n configs
- n8n_executor.py: N8N-style workflow execution with connections
- node_executor.py: Individual node execution with plugin dispatch
- loop_executor.py: Loop node execution with iteration control
- execution_order.py: Topological sort for node ordering

Schema & Validation:
- n8n_schema.py: N8N workflow schema types and validation
- n8n_converter.py: Legacy to n8n schema conversion

Plugin System:
- plugin_loader.py: Dynamic plugin loading
- plugin_registry.py: Plugin discovery and registration
- plugin_map.json: 116 plugin type mappings

Runtime & Context:
- runtime.py: Workflow runtime container
- input_resolver.py: Binding and coercion resolution
- value_helpers.py: Value normalization helpers
- workflow_context_builder.py: Runtime context assembly
- workflow_config_loader.py: Configuration loading
- workflow_engine_builder.py: Engine assembly with dependencies

Utilities:
- tool_calls_handler.py: LLM tool call handling
- tool_runner.py: Tool execution with logging
- notification_helpers.py: Slack/Discord notifications
- workflow_adapter.py: N8N format handling
- workflow_graph.py: Node/edge graph for visualization

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

workflow/executor/python/workflow_engine_builder.py

@@ -0,0 +1,25 @@
+"""Build workflow engine with dependencies."""
+from .engine import WorkflowEngine
+from .input_resolver import InputResolver
+from .loop_executor import LoopExecutor
+from .node_executor import NodeExecutor
+from .plugin_registry import PluginRegistry, load_plugin_map
+from .runtime import WorkflowRuntime
+from .tool_runner import ToolRunner
+
+
+def build_workflow_engine(workflow_config: dict, context: dict, logger):
+    """Assemble workflow engine dependencies."""
+    runtime = WorkflowRuntime(context=context, store={}, tool_runner=None, logger=logger)
+    # Only create ToolRunner if tool_map and msgs are provided (needed for AI workflows)
+    if "tool_map" in context and "msgs" in context:
+        tool_runner = ToolRunner(context["tool_map"], context["msgs"], logger)
+        runtime.tool_runner = tool_runner
+
+    plugin_registry = PluginRegistry(load_plugin_map())
+    input_resolver = InputResolver(runtime.store)
+    loop_executor = LoopExecutor(runtime, input_resolver)
+    node_executor = NodeExecutor(runtime, plugin_registry, input_resolver, loop_executor)
+    loop_executor.set_node_executor(node_executor)
+
+    return WorkflowEngine(workflow_config, node_executor, logger, runtime, plugin_registry)