feat: Implement OAuth flow for MCP server integration

- Added MCPOAuthManager to handle OAuth authorization.
- Updated MCPServerSave resource to manage OAuth status and callback.
- Introduced new endpoints for OAuth status and callback handling.
- Enhanced user interface to support OAuth authentication type.
- Implemented polling mechanism for OAuth status in MCPServerModal.
- Updated frontend services and endpoints to accommodate new OAuth features.
- Improved error handling and user feedback for OAuth processes.

frontend/src/api/endpoints.ts

@@ -59,6 +59,8 @@ const endpoints = {
     MANAGE_SOURCE_FILES: '/api/manage_source_files',
     MCP_TEST_CONNECTION: '/api/mcp_server/test',
     MCP_SAVE_SERVER: '/api/mcp_server/save',
+    MCP_OAUTH_STATUS: (task_id: string) =>
+      `/api/mcp_server/oauth_status/${task_id}`,
   },
   CONVERSATION: {
     ANSWER: '/api/answer',