fix: handle missing 'env' attribute in MCP server Prisma model (#12560)

- Use getattr() with default value when accessing mcp_server.env
- Prevents AttributeError when Prisma doesn't include the field
- Fixes startup error: 'LiteLLM_MCPServerTable' object has no attribute 'env'

The issue occurs when Prisma fetches records and doesn't include
null/undefined fields in the returned object.

litellm/proxy/_experimental/mcp_server/mcp_server_manager.py

@@ -160,7 +160,9 @@ class MCPServerManager:
             _mcp_info: MCPInfo = mcp_server.mcp_info or {}
             
             # Use helper to deserialize environment dictionary
-            env_dict = _deserialize_env_dict(mcp_server.env)
+            # Safely access env field which may not exist on Prisma model objects
+            env_data = getattr(mcp_server, 'env', None)
+            env_dict = _deserialize_env_dict(env_data)
             
             new_server = MCPServer(
                 server_id=mcp_server.server_id,