feat: Implement file download token management and restructure file routes

- Added DownloadTokenManager for creating and verifying JWT download tokens.
- Introduced new download routes for creating download tokens and downloading files using tokens.
- Restructured file upload routes into a dedicated sub-router.
- Updated file upload session management with improved error handling and response structures.
- Created a new MCP (Microservice Communication Protocol) router with basic request and response models.
- Added base models for MCP requests and responses, including method enumeration.

models/model_base.py

@@ -0,0 +1,39 @@
+import uuid
+from enum import StrEnum
+
+from sqlmodel import Field
+
+from .base import SQLModelBase
+
+class MCPMethod(StrEnum):
+    """MCP 方法枚举"""
+
+    PING = "ping"
+    """Ping 方法，用于测试连接"""
+
+class MCPBase(SQLModelBase):
+    """MCP 请求基础模型"""
+    
+    jsonrpc: str = "2.0"
+    """JSON-RPC 版本"""
+
+    id: uuid.UUID = Field(default_factory=uuid.uuid4)
+    """请求/响应 ID，用于标识请求/响应的唯一性"""
+
+class MCPRequestBase(MCPBase):
+    """MCP 请求模型基础类"""
+
+    method: str
+    """方法名称"""
+
+class MCPResponseBase(MCPBase):
+    """MCP 响应模型基础类"""
+
+    result: str
+    """方法返回结果"""
+
+class ResponseBase(SQLModelBase):
+    """通用响应模型"""
+
+    instance_id: uuid.UUID = Field(default_factory=uuid.uuid4)
+    """实例ID，用于标识请求的唯一性"""