feat(06-03): export Pipeline class from pipeline package

- Add Pipeline import from kb_workflow.pipeline.pipeline
- Add Pipeline to __all__ exports list
- Enables: from kb_workflow.pipeline import Pipeline

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

kb_workflow/pipeline/__init__.py

@@ -26,6 +26,7 @@ from kb_workflow.pipeline.retry import retry_on_network_error
 from kb_workflow.pipeline.link_parser import LinkParser, ParsedLink
 from kb_workflow.pipeline.idempotency import IdempotencyChecker
 from kb_workflow.pipeline.platforms import PlatformAdapter, BilibiliAdapter, ZhihuAdapter
+from kb_workflow.pipeline.pipeline import Pipeline
 
 __all__ = [
     # Schemas
@@ -59,6 +60,8 @@ __all__ = [
     "PlatformAdapter",
     "BilibiliAdapter",
     "ZhihuAdapter",
+    # Pipeline
+    "Pipeline",
 ]
 
 __version__ = "0.1.0"