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.

routers/api/v1/mcp/__init__.py

@@ -0,0 +1,19 @@
+from fastapi import APIRouter
+
+from models import MCPRequestBase, MCPResponseBase, MCPMethod
+
+# MCP 路由
+MCP_router = APIRouter(
+    prefix='/mcp',
+    tags=["mcp"],
+)
+
+@MCP_router.get(
+        "/",
+)
+async def mcp_root(
+    param: MCPRequestBase
+):
+    match param.method:
+        case MCPMethod.PING:
+            return MCPResponseBase(result="pong", **param.model_dump())