refactor(06-01): update platform adapters to use standard imports

- Remove sys.path manipulation from bilibili.py and zhihu.py
- Use standard imports from kb_workflow.metadata
- Remove try/except wrappers around imports

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

kb_pipeline/platforms/bilibili.py

@@ -18,7 +18,6 @@ import asyncio
 import logging
 import os
 import re
-import sys
 import tempfile
 from pathlib import Path
 from typing import Dict, Any, Optional
@@ -27,21 +26,10 @@ from .base import PlatformAdapter
 from ..errors import NetworkError, AuthError
 from ..retry import retry_on_network_error
 from ..state import WorkflowStateManager
+from kb_workflow.metadata.bilibili_extractor import BilibiliExtractor
 
 logger = logging.getLogger(__name__)
 
-# Add kb-bilibili-metadata to path if not installed as package
-_BILIBILI_METADATA_PATH = Path(__file__).parent.parent.parent / "kb-bilibili-metadata"
-if _BILIBILI_METADATA_PATH.exists():
-    sys.path.insert(0, str(_BILIBILI_METADATA_PATH))
-
-try:
-    from bilibili_extractor import BilibiliExtractor
-    BILIBILI_EXTRACTOR_AVAILABLE = True
-except ImportError:
-    BILIBILI_EXTRACTOR_AVAILABLE = False
-    BilibiliExtractor = None
-
 
 class BilibiliAdapter(PlatformAdapter):
     """Bilibili platform adapter for video and article content
@@ -86,12 +74,6 @@ class BilibiliAdapter(PlatformAdapter):
             timeout: Request timeout in seconds (default 30)
             state_manager: Optional WorkflowStateManager for recording step status
         """
-        if not BILIBILI_EXTRACTOR_AVAILABLE:
-            raise ImportError(
-                "BilibiliExtractor not available. "
-                "Ensure kb-bilibili-metadata/bilibili_extractor.py is accessible."
-            )
-
         self._extractor = BilibiliExtractor(headless=headless, timeout=timeout)
         self._state_manager = state_manager