refactor(01-01): export WorkflowStateManager from kb_pipeline

Add WorkflowStateManager to package exports for easier imports.
Users can now use: from kb_pipeline import WorkflowStateManager

All 20 tests pass with 90% coverage.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

kb_pipeline/__init__.py

@@ -12,6 +12,7 @@ from .schemas import (
     WorkflowState,
     StepDefinition,
 )
+from .state import WorkflowStateManager
 
 __all__ = [
     "StepInput",
@@ -21,6 +22,7 @@ __all__ = [
     "StepRecord",
     "WorkflowState",
     "StepDefinition",
+    "WorkflowStateManager",
 ]
 
 __version__ = "0.1.0"