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

---------

Co-authored-by: Mario Zechner <badlogicgames@gmail.com>

packages/ai/test/cross-provider-handoff.test.ts

@@ -113,6 +113,7 @@ const PROVIDER_MODEL_PAIRS: ProviderModelPair[] = [
 	{ provider: "mistral", model: "devstral-medium-latest", label: "mistral-devstral-medium" },
 	// MiniMax
 	{ provider: "minimax", model: "MiniMax-M2.7", label: "minimax-m2.7" },
+	{ provider: "minimax-cn", model: "MiniMax-M2.7", label: "minimax-m2.7" },
 	// OpenCode Zen
 	{ provider: "opencode", model: "big-pickle", label: "zen-big-pickle" },
 	{ provider: "opencode", model: "claude-sonnet-4-5", label: "zen-claude-sonnet-4-5" },
@@ -123,6 +124,8 @@ const PROVIDER_MODEL_PAIRS: ProviderModelPair[] = [
 	// OpenCode Go
 	{ provider: "opencode-go", model: "kimi-k2.5", label: "go-kimi-k2.5" },
 	{ provider: "opencode-go", model: "minimax-m2.5", label: "go-minimax-m2.5" },
+	// Xiaomi MiMo
+	{ provider: "xiaomi", model: "mimo-v2.5-pro", label: "xiaomi-mimo-v2.5-pro" },
 ];
 
 // Cached context structure