chore: simayi-approved changes - lint fixes, toolchain improvements, healthz

All changes reviewed and APPROVED in PR #12 (Review ID: 40):
- toolchain_routes: webhook repo/org format compat, content dedup (sha256), closed issue filter
- dispatcher: inform mail crash 误标 done 修复
- ticker: cleanup and improvements
- healthz endpoint
- conftest: integration/e2e deselect markers
- docs: design docs, test-guide updates
- various lint/whitespace fixes across 30 files

src/blackboard/operations.py

@@ -11,6 +11,7 @@ from typing import Any, Dict, List, Optional
 
 from .db import (
     VALID_TRANSITIONS,
+    VALID_STATUSES,
     COMMENT_TYPES,
     EVENT_TYPES,
     OUTPUT_TYPES,
@@ -692,6 +693,7 @@ class Blackboard:
         finally:
             conn.close()
 
+
     # ── Checkpoint CRUD（M3） ──
 
     def create_checkpoint(