feat(06-01): create metadata directory and move bilibili modules

- Rename kb-workflow to kb_workflow for Python package compatibility
- Move bilibili_extractor.py and bilibili_metadata.py to kb_workflow/metadata/
- Create metadata/__init__.py with BilibiliExporter export

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

kb_workflow/.env

@@ -0,0 +1,14 @@
+# KB Workflow 环境变量配置
+export KB_BASE_PATH="~/work/knowledge-base"
+
+# 可选: B站 Cookie（用于下载会员视频）
+# export BILIBILI_COOKIE="SESSDATA=xxx; bili_jct=xxx"
+
+# 可选: AI 分析配置
+# export AI_API_KEY="your-api-key"
+# export AI_PROVIDER="openai"  # 或 zhipu, minimax
+# export AI_MODEL="gpt-4"
+
+# 可选: Git 配置
+# export KB_GIT_USER="Your Name"
+# export KB_GIT_EMAIL="your@email.com"