Replace standalone 'Token Plan' section with general Xiaomi MiMo
section using the built-in xiaomi_mimo provider. Token plan becomes
a note within the section, since it's just an apiBase override.
Key changes:
- Use xiaomi_mimo provider (auto-matches via 'mimo' keyword in model name)
- Drop redundant provider field (auto-detected)
- Add token plan tip to provider tips block
- Restructure as general Xiaomi MiMo section with token plan as note
honjiaxuanandXubin Ren