feat(xiaomi): add Xiaomi MiMo as first-class provider

Cherry-picked from PR #7702 by kshitijk4poor.

Adds Xiaomi MiMo as a direct provider (XIAOMI_API_KEY) with models:
- mimo-v2-pro (1M context), mimo-v2-omni (256K, multimodal), mimo-v2-flash (256K, cheapest)

Standard OpenAI-compatible provider checklist: auth.py, config.py, models.py,
main.py, providers.py, doctor.py, model_normalize.py, model_metadata.py,
models_dev.py, auxiliary_client.py, .env.example, cli-config.yaml.example.

Follow-up: vision tasks use mimo-v2-omni (multimodal) instead of the user's
main model. Non-vision aux uses the user's selected model. Added
_PROVIDER_VISION_MODELS dict for provider-specific vision model overrides.
On failure, falls back to aggregators (gemini flash) via existing fallback chain.

Corrects pre-existing context lengths: mimo-v2-pro 1048576→1000000,
mimo-v2-omni 1048576→256000, adds mimo-v2-flash 256000.

36 tests covering registry, aliases, auto-detect, credentials, models.dev,
normalization, URL mapping, providers module, doctor, aux client, vision
model override, and agent init.

hermes_cli/auth.py

@@ -250,6 +250,14 @@ PROVIDER_REGISTRY: Dict[str, ProviderConfig] = {
         api_key_env_vars=("HF_TOKEN",),
         base_url_env_var="HF_BASE_URL",
     ),
+    "xiaomi": ProviderConfig(
+        id="xiaomi",
+        name="Xiaomi MiMo",
+        auth_type="api_key",
+        inference_base_url="https://api.xiaomimimo.com/v1",
+        api_key_env_vars=("XIAOMI_API_KEY",),
+        base_url_env_var="XIAOMI_BASE_URL",
+    ),
 }
 
 
@@ -908,6 +916,7 @@ def resolve_provider(
         "opencode": "opencode-zen", "zen": "opencode-zen",
         "qwen-portal": "qwen-oauth", "qwen-cli": "qwen-oauth", "qwen-oauth": "qwen-oauth",
         "hf": "huggingface", "hugging-face": "huggingface", "huggingface-hub": "huggingface",
+        "mimo": "xiaomi", "xiaomi-mimo": "xiaomi",
         "go": "opencode-go", "opencode-go-sub": "opencode-go",
         "kilo": "kilocode", "kilo-code": "kilocode", "kilo-gateway": "kilocode",
         # Local server aliases — route through the generic custom provider