* fix(sse): recognize xiaomi-tokenplan mimo as a thinking-mode model (port from 9router#1321)
The reasoning_content injector already handles DeepSeek/Kimi/K2/MiniMax thinking-mode upstreams, echoing a placeholder reasoning_content on assistant turns that lack one. Its THINKING_MODEL_PATTERNS list omitted the xiaomi-tokenplan mimo family, so requests through xiaomi-tokenplan/mimo-v2.5-pro still hit upstream's 400 'reasoning_content in the thinking mode must be passed back to the API', making the model unusable in multi-turn conversations (e.g. Codex CLI). Add a /\bmimo\b/i pattern so mimo models get the same treatment.
Reported-by: z.wl (@xxue-z) (https://github.com/decolua/9router/issues/1321)
* docs(changelog): add fragment for #7098 mimo thinking-model fix
