0.1.0: Integrate Notion MCP as core operation layer

- New MCP client (src/mcp_notion_client.py) for Notion API calls
- Route all Notion operations through MCP protocol
- Update notion_integration.py to use MCP instead of direct SDK
- Refactor setup_notion_databases.py to use MCP
- Add mcp>=1.0.0 to requirements.txt
- Update README with MCP architecture documentation