Add the loading page to the React UI

where the logo is at https://github.com/IBM/mcp-context-forge/blob/epic/ui-rewrite/client/src/components/icons/MainNavIcon.tsx

NOTE: Make sure that the feature branch is created from the epic/ui-rewrite branch and the PR is created against the epic/ui-rewrite branch.