feat(provider): add Xiaomi MiMo LLM support

Register xiaomi_mimo as an OpenAI-compatible provider with its API base URL,
add xiaomi_mimo to the provider config schema, and document it in README.

Signed-off-by: Lingao Meng <menglingao@xiaomi.com>

nanobot/providers/base.py

@@ -49,7 +49,7 @@ class LLMResponse:
     tool_calls: list[ToolCallRequest] = field(default_factory=list)
     finish_reason: str = "stop"
     usage: dict[str, int] = field(default_factory=dict)
-    reasoning_content: str | None = None  # Kimi, DeepSeek-R1 etc.
+    reasoning_content: str | None = None  # Kimi, DeepSeek-R1, MiMo etc.
     thinking_blocks: list[dict] | None = None  # Anthropic extended thinking
     
     @property

nanobot/providers/registry.py

@@ -297,6 +297,15 @@ PROVIDERS: tuple[ProviderSpec, ...] = (
         backend="openai_compat",
         default_api_base="https://api.stepfun.com/v1",
     ),
+    # Xiaomi MIMO (小米): OpenAI-compatible API
+    ProviderSpec(
+        name="xiaomi_mimo",
+        keywords=("xiaomi_mimo", "mimo"),
+        env_key="XIAOMIMIMO_API_KEY",
+        display_name="Xiaomi MIMO",
+        backend="openai_compat",
+        default_api_base="https://api.xiaomimimo.com/v1",
+    ),
     # === Local deployment (matched by config key, NOT by api_base) =========
     # vLLM / any OpenAI-compatible local server
     ProviderSpec(