Enhance knowledge base functionality and integrate S3 storage support

- Add new models for `KnowledgeDocument` and `KnowledgeChunk` to manage document ingestion and chunking.
- Implement S3-compatible storage integration for knowledge documents, allowing for file uploads and retrieval.
- Introduce API endpoints for managing knowledge bases and documents, including creation, deletion, and searching.
- Update frontend components to support knowledge base configuration and document management, improving user interaction.
- Enhance backend services for knowledge processing and retrieval, ensuring robust handling of document statuses and errors.

backend/requirements.txt

@@ -24,3 +24,8 @@ sqlalchemy[asyncio]>=2.0
 alembic>=1.13
 asyncpg
 greenlet  # SQLAlchemy 异步运行时必需(部分平台不会自动带上)
+pgvector
+boto3
+python-multipart
+pypdf
+python-docx