CLI / TUI cosmetics

Add fun stuff:
- Loading animations for HTTP I/O (waving flag?)
- OAuth callback template consistent with Flagsmith UI, and maybe an emoji or two

Start by locating the CLI's HTTP I/O handling and OAuth callback template or rendering entry point. Clarify which loading animation and Flagsmith UI styling are wanted, then consider the work complete when the chosen animation appears during HTTP operations and the callback output matches the agreed template, including any approved emoji.

索引モデルが issue の本文から書いたものです。