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/.env.example

@@ -12,6 +12,15 @@ PORT=8000
 # 前端开发地址,允许跨域(公网部署时加上实际前端 origin)
 CORS_ORIGINS=http://localhost:3000,http://127.0.0.1:3000
 
+# ---- RustFS / S3-compatible storage ----
+S3_ENDPOINT_URL=http://localhost:9000
+S3_ACCESS_KEY=rustfsadmin
+S3_SECRET_KEY=rustfsadmin
+S3_BUCKET=ai-video
+S3_REGION=us-east-1
+KNOWLEDGE_MAX_FILE_BYTES=20971520
+KNOWLEDGE_TOP_K=5
+
 # ---- WebRTC TURN(公网跨网语音预览;本地开发留空) ----
 # 与 docker compose --profile remote 的 coturn 配套。云安全组需放行 UDP 3478 与 49152-49200。
 # PUBLIC_IP 填云主机公网 IP(compose 里给 coturn --external-ip 用,见项目根 .env)。