feat(ai): add Xiaomi MiMo provider (#4005)
* fix(ai): include minimax-cn in cross-provider-handoff matrix
* feat(ai): add Xiaomi MiMo provider
Adds Xiaomi MiMo as an openai-completions-compatible provider.
- packages/ai: register provider in types/KnownProvider, env-api-keys (XIAOMI_API_KEY), generate-models, models.generated.ts, overflow util, README, CHANGELOG
- packages/ai/test: extend stream, tokens, abort, empty, context-overflow, overflow, image-tool-result, tool-call-without-result, total-tokens, unicode-surrogate, cross-provider-handoff matrices with Xiaomi
- packages/coding-agent: default model (mimo-v2.5-pro), display name (Xiaomi MiMo), CLI env var docs, README, docs/providers.md
closes #3912
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Co-authored-by: Mario Zechner <badlogicgames@gmail.com>